Your Xfinity username is part of your Xfinity ID, which you can use to sign in. It's also your @comcast.net email handle.

You can change your Xfinity ID at any time in My Account - however, your old Xfinity ID can’t be used again.

Sign in to My Account.
Click the Users tab at the top of the page.
Click Edit next to the user's name that you’d like to change.
Note: The primary user can edit any user’s name, but a manager and/or member may only edit their own. Viewers can't edit any user’s name, including their own.

In the Xfinity ID & Password section, click Edit to the right of the current Username.
Confirm the password and enter the new Xfinity ID in the New Username box, then click Save.
Note: If you are changing the Xfinity ID for another user on your account, you’ll need to enter their password, not your own. This will also change the @comcast.net email.
A confirmation message will appear.

If you want more details on your Xfinity ID and instructions on how to set it up, check out Learn about Xfinity ID and Create an Xfinity ID, or chat with us.