There will be times when you need to change your locks either due to them not working any longer, moving into a new house, kicking your partner out!!, or other security reasons.

Most houses with a wooden front door will have two lock types on it. A "Yale" type rim lock , and a "Chubb" type mortice lock. It can be quite expensive getting a lock-smith out for this, however they are quite easy to change yourself. All you need is a few hand tools.

UPVC front doors will normally have a some what different euro-cylinder lock

Changing the cylinder on a front door(rim) lock
Changing a mortice lock
Changing the lock on a UPVC door