We've got just the article for you
You need to fill out the form and take it to an Xfinity Retail store for them to make the change.
Or you could have your roommate disconnect and you can set up new services.
You'll have to return it and they would get a new one.
You're currently the account holder, meaning if anything happens (eg if you straight up let thempay the bills, and they are delinquent, it becomes your financial and credit liability).
You can either fill out the form, bring it to the Xfinity store and have the name changed from yours to theirs (so they assumes financial responsibility) and you maintain service continuity, or you can have them sign up for service and set a date so there's overlap, or simply go to the retail store and they can do a disconnect and set you up with new services and provide you the equipment on the spot.