Please see https://www.xfinity.com/support/articles/updating-your-mailing-address. You can't change this yourself, you need to have a Comcast rep make the change for you.
If an Employee doesn't reply to your message here contact a phone rep at 1-800-Comcast, or see https://www.xfinity.com/support/contact-us. If you decide to visit a Service Center or Xfinity Store check hours and locations at https://www.xfinity.com/support/service-center-locations.
Note that, when you move, your account number changes and the logins/email addresses from the previous account number may or may not be transferred to the new one.