How to remove a number from an iphone 4 and replace it with another number?

I have a verizon iphone and it has a number on it already and it isn't in use. I have another verizon phone and i want to put that number on the iphone. Is there a way i can put the number on that phone even when there's a different number already on there. Or can i remove the old number?

Got a verizon kiosk they might be able to do that for you