What rekeying does
Rekeying changes the internal pins of an existing cylinder so it works with a new key. The lock body stays on the door.
It suits locks that are in good working order when the concern is who holds keys — for example after moving house, a tenancy changeover or staff leaving.
When replacement is the better choice
Replace the lock if it is worn, damaged, stiff even after servicing, or no longer suits how the door is used.
Replacement is also the path when you want a different type of lock, such as adding a deadlock, or better quality hardware.
Questions to ask before deciding
Is the lock turning smoothly? Is the door aligned with the strike? Do you want several doors on one key? Are there strata or lease rules about the lock?
Photos of the lock face and the edge of the door help a locksmith advise you before a visit.