Unplug your freezer as a safety precaution.
Unscrew the screws from the existing lock. The lock should be in two parts. One part will be screwed to the door of the freezer and the other to the body of the freezer. The way in which the lock actually works will depend on the type. Some have a simple latch that connects and locks the two parts with a key. Others have a separate lock that connects the two parts.
Organize your new lock kit. Make sure you have all the parts and screws that you will need to attach the lock to your freezer. Ideally, you will want a lock that is similar to the one you are replacing, so you will be able to use the same holes to attach the two parts of the lock to the freezer.
Attach the new lock to the freezer with the appropriate parts and the screwdriver. Make sure you are attaching the correct part to the door and the correct part to the body of the freezer. Make sure the lock is securely connected and could not be easily removed.
Plug your freezer in and test your new lock by locking and unlocking it several times. Make sure that it locks and unlocks smoothly and without damaging the freezer. Put any keys to the lock in a safe place that you will remember.