How to Change a Lock: Replace a Door Lock Step by Step

Changing a lock replaces the lock hardware, keys, or both. It can restore reliable operation or prevent an old key from working, such as after moving into a home. This guide covers common keyed entry and privacy locks with a round knob or lever and a separate latch. Lock designs vary, so use the replacement manufacturer’s instructions whenever they differ from these general steps.

Before starting, confirm that you are authorized to change the lock. If you rent, check with the property owner or manager first. For an exterior door, maintain a secure alternative entrance while the door is open, and do not leave the property unattended. A locksmith is a better choice if the hardware is damaged, the door has a multipoint or mortise lock, or the replacement does not match the existing door preparation.

What You’ll Need

A replacement lock set that matches the door’s thickness, backset, bore, and intended use
A screwdriver that fits the lock’s screws; check whether the replacement calls for a Phillips or flat-head type
A tape measure or ruler
A pencil and a small flashlight, if needed
The new lock’s keys and installation instructions

“Backset” is the distance from the edge of the door to the center of the knob or lever hole. Common residential locks may use a 2⅜-inch or 2¾-inch backset, but measure rather than assume. Also check the door thickness and the diameter of the existing cross-bore. The replacement’s packaging or instructions list the sizes it fits.

Step-by-Step

Identify the lock type. Look at both sides of the door and its edge. This process is for a typical cylindrical lock with a latch that slides into the door frame. A deadbolt is usually a separate, larger lock and may require different steps; a mortise lock has a larger case fitted into the door edge. Do not force a standard replacement into either style.
Measure and choose a match. Measure the door thickness, backset, and bore diameter, then compare them with the replacement specifications. Check that the latch length and faceplate style suit the existing opening. For an exterior door, choose a keyed entry set intended for exterior use. A privacy lock for a bedroom or bathroom is not a substitute for a secure keyed lock.
Keep the door open. Open the door fully and make sure it cannot swing shut while you work. Keep the keys and replacement instructions close by. Do not remove the existing lock until you have confirmed the new set is complete and compatible.
Remove the inside trim. Find the screws on the interior side of the knob or lever. Support the outside hardware with one hand while loosening the screws with the other. If no screws are visible, look for a small release slot or detent and follow the manufacturer’s removal directions; do not pry at the trim with force. Remove the interior and exterior pieces carefully.
Take out the latch. Remove the two screws in the plate on the door edge. Pull the latch straight out. Note which way its sloped face points: it should face the direction the door closes so it can ride over the strike plate. If the new latch has an adjustable backset, set it to the measurement you took.
Fit the new latch. Slide it into the edge bore with the correct orientation and seat the faceplate flush against the door. The latch bolt should move freely. Align the screw holes and secure the plate with the supplied screws, tightening until snug without stripping the screw heads or crushing the wood.
Install the exterior half. Place the keyed or exterior side through the door bore, aligning its spindle or connecting parts with the latch mechanism. Keep the keyway in the intended upright position and make sure the hardware sits flat against the door. Some models have a particular spindle orientation, so follow the included diagram.
Attach the interior half. Fit the inside knob or lever onto the spindle and align the mounting holes. Start both screws by hand, then tighten them evenly. The two sides should sit flush and stable; avoid overtightening, which can bind the mechanism or damage the door.
Check the strike plate and operation. With the door still open, turn the knob or lever and test the key, thumb turn, or privacy button as applicable. The latch should retract fully and spring back without sticking. Close the door gently and check that the latch enters the strike plate. If it catches, inspect alignment before forcing the door.
Secure the keys and old parts. Once the lock works smoothly with the door both open and closed, keep the new keys in a safe place and give authorized occupants a copy as appropriate. Dispose of or store the old hardware so it cannot be mistaken for the current lock.

Common Mistakes

Buying by appearance alone: Similar-looking locks can have different backsets, door-thickness limits, or mounting arrangements. Measure and check the product specifications first.
Installing the latch backward: If the sloped bolt faces the wrong way, the door may not close smoothly. Orient it as shown in the instructions.
Closing the door too soon: A misaligned or stuck latch can leave you locked out. Test every control with the door open before trying it closed.
Overtightening the screws: Excess force may strip screw heads, distort the hardware, or make a knob bind. Tighten evenly until secure, not excessively tight.
Assuming a new lock changes every access point: Replacing a knob does not necessarily change a separate deadbolt, garage entry, or other keyed lock. Identify and address each lock that needs a new key.

Tips

Photograph the old lock’s orientation before removing it; the image can help you compare the latch and spindle arrangement.
Keep screws and small parts together, and avoid mixing old and new components unless the manufacturer specifically says they are compatible.
If you only need to prevent old keys from working, ask whether the lock can be rekeyed. Rekeying changes the key combination without replacing the whole lock, but it is not possible or practical for every model.
For a keyed exterior lock, check that the key turns smoothly and that the inside thumb turn or lever operates freely. Confirm the door can be secured from the intended side.
Keep any instructions, spare keys, and model information together for future maintenance or replacement.

Troubleshooting

The lock will not fit: Stop rather than enlarging holes or forcing parts. Recheck the backset, door thickness, bore size, and lock type. Return or exchange the hardware for a compatible model, or ask a locksmith if the door has an unusual preparation.

The knob or lever binds: Loosen the mounting screws slightly and test again. If it frees up, retighten evenly. Check that the latch and spindle are aligned and that the latch moves freely when the trim is removed. If the mechanism still sticks, take it apart according to the instructions and inspect for a wrongly oriented or incompatible part.

The latch does not line up with the frame: Look for a loose strike plate, a latch installed backward, or a door that is sagging. Confirm the latch works with the door open. If it works open but catches closed, adjust the strike plate only if you can do so without compromising the frame; otherwise get help rather than forcing the door.

The key will not turn or the door will not unlock: Do not force the key, which can bend or break it. Check that you are using a key supplied for that lock and that the door is not pressing hard against the latch. If the lock remains stuck, contact a locksmith.

Frequently Asked Questions

Can I change a door lock myself?

Many standard cylindrical locks can be replaced with basic tools if the new set matches the door. Unusual, damaged, or integrated locking systems may need a locksmith.

How do I know which replacement lock to buy?

Measure the backset, door thickness, and bore, then match those measurements to the product specifications. Also make sure the lock type and intended use fit the door.

Is changing a lock the same as rekeying it?

No. Changing a lock replaces its hardware, while rekeying changes which key operates a compatible lock. A locksmith can tell you whether rekeying is an option for your model.

Should I change the locks after moving?

It is sensible to make sure only authorized people can operate the locks, but changing hardware is not always necessary. A compatible lock may be rekeyed instead; consider every exterior lock, not just the front door.

What if the replacement lock uses different screw holes?

Do not force screws into misaligned holes or leave the lock loosely attached. Check the installation instructions and compatibility; if the door needs modification, have a qualified locksmith handle it.

Can I replace a deadbolt using these steps?

Not necessarily. Deadbolts have different parts and installation details, so use the instructions for that specific model and verify its measurements. If the existing lock is a mortise or multipoint system, get professional help.

Further reading: Associated Locksmiths of America. Details can change, so check the official page for anything that matters to you. Spotted a mistake? Tell us. How we write an answer.