Not much. Let Xfinity know you'll be moving and they'll help transfer your account to the new address. It's a good idea to choose an activation date/time at the new address that slightly overlaps with the disconnection of the current so you'll never be without internet. Setup the same equipment at the new address and once activated, you're good to go. Billing won't change unless you're moving hundreds of miles and the new region has slightly different plans available.