- Sign in to My Account on your phone/pc browser. - Next, go to the Users tab located at the top of the page. - Then, click the Edit option next to the user's name you wish to change. - Under the Xfinity ID & Password section, tap the Edit option on the right side of the current Username. - After that, confirm the password and enter the new Xfinity ID in the New Username box.  - Finally, tap the Save option. You will see a confirmation message.