You have to get a new lock when you replace it.
There are several factors to consider when trying to determine which lock to replace the old lock with. Some of these factors include the budget you are using and the preferences and features you need in your lock. For example, if you want to change the lock from a Euro Cylinder lock to a mortise lockset, you cannot use rekeying as a solution. Once you have determined your lock, you can pick it up from your local hardware store or buy it from the locksmith.
The main difference between replacing a lock and relocking is that you will now use a completely different (and possibly brand new) lock. Replacing a lock usually means that the entire lock body will be different. This is a more expensive process than relocking the lock, but it does have its benefits. The main reason why it is more expensive is simply because you will have to get a new lock for the door when you replace it.