Things You'll Need
Instructions
Turn on your 360 console by pressing the power button on the faceplate. Alternately, hold down the silver Xbox button at the center of the controller until the console turns on.
Allow the Live service to log your in your gamertag. Scroll to the "My Xbox" window with the controller.
Choose "Change Gamertag." Navigate to the "Select New Gamertag" option. If your choice is not available, view the "Get Suggestions" option to select from alternatives.
Enter your new gamertag using the on-screen QWERTY keyboard, navigating from character to character with the controller. Select each character with the "A" button on the controller. Press "Start" when complete.
Choose "Yes, Use this Gamertag" when presented with the option. The system will log your out, then back in with the new gamertag. Your achievements are carried with the new tag.