A Yale-Type cylinder lock is popular for several reasons. These locks are hard to pick, you can open them from inside without a key, and you can deadlock them too. Unfortunately, unless you deadlock them a thief can enter if they have a key. This is why it is always best to change the cylinder in a Yale lock, if in doubt, and definitely when you move to a new home. If things go well you will not need to find a locksmith. If not, then there is always Mr-Skill.
o First remove the lockbox inside the door – this is the piece that houses the bolt itself, the deadlock and the turning handle. Simply remove the screws attaching it to the door, and wiggle it off carefully.
o When you have done this, you will see a metal backing plate with two screws passing through it. These go through the door and hold the lock in place that you are going to change. Remove these screws. They are usually made of brass, so take care not to strip the heads.
o Push the barrel gently out through the door and catch it on the outside before it falls and chips your tiles. If you cannot release the lock, try tapping gently.
o Compare the old and new lock. If the thin wobbly metal bars are different lengths then trim the new one accordingly, by snapping it off at an appropriate groove. Re-assemble the lock using the new lock cylinder in the reverse order. Store the spare key somewhere safe.