box upgrade - XFinity

This question is about "box upgrade", with XFinity-Comcast television equipment. We received your letter notifying us to update our tv boxes. We have updated 2 of our 3 boxes. The remaining box is part of our complex system which will require us to make an appointment with our AV specialist. For this reason we will need the new box before returning the old one. How do we do this without incurring additional charges from xfinity?

The this topic covered box upgrade, and XFinity - Comcast cable tv service.