I just got off the phone with vzw customer support.... the lady I talked to about it said that I (we) could do any of the three... go into a store, call in to customer support or do it online via the "Activate or Switch device" button.
She said all we had to do was activate my (our) new iPhone 5(s), so its active on the new line, then do one of the above three methods, answer a few questions and then the phone will be switched to what ever line you want it on. At that point, sell your old iPhone and start enjoying your iPhone 5.