You have an old car, and you want to renew it. If you buy it brand new and toss the old one, you are destroying the old one. If you keep changing pieces of it, testing them to see they work, and keep going until you have replaced the whole car, it's still the old car, just brand new.
There's not much difference at the end, except that you can consider that the second way of doing things will let you still use the old car, only it'll be new.
There's not much difference at the end, except that you can consider that the second way of doing things will let you still use the old car, only it'll be new.