Question: How can we change and install the lock?
Option 0: Purchase your new lock, remove the deadbolt only, insert the new deadbolt nd leave the old dead lock on the door, then test the old deadlock to see if it works with the new deadbolt.
Option 1: Purchase your new lock, remove the old lock and deadbolt, insert the new deadbolt first, then insert the new dead bolt lock then test the new lock.
Answer: 1