well when you buy and receive the phone, all you need to do is call verizon and tell them that you want to replace your phone with one that you already have. They'll then ask you to take the battery off the new phone and read to them the numbers on the sticker in the back. Once this is done, all you need to do is call a specific number that they give you on the new phone, and thats it! its done...
You can do that, or take it to a verizon store and they'll do it for you, and they'll even transfer your contacts aswell.