Instructions
Open the system tray and take out any games or DVDs to avoid auto-booting.
Choose the Live-activated profile you wish to change.
Highlight "Edit Gamer Profile, Gamertag" and press the "A" button.
Select "Change and personalize your gamertag on Xbox Live" from the menu.
Highlight "Continue" and press the "A" button, then enter the desired name change with the on-screen keyboard.
Press the "Start" button or highlight "Done," then press the "A" button. This will check your name against taken names to ensure it is unique.
Press the "B" button to try again if your name is taken.
Select "Confirm" to purchase your new gamertag.