Things You'll Need
Instructions
Sign into your X-Box Live enabled account from your X-Box 360's start-up dashboard.
Select "My Xbox" from the dashboard; press the A button.
Select "Change Gamertag" from the menu that opens, then press the A button.
Select "Get Suggestions," and press the A button for a name to be generated for you. You will not be required to accept this name.
Select "Enter New Gamertag" and press the A button to create your own tag.
Enter the name you prefer using the on-screen keyboard that pops up.
Select "Yes, use this gamertag" and confirm that you wish to spend 800 Microsoft points on your new name.