Instructions
Turn on your Xbox 360, and select the gamertag with the avatar you wish to customize.
Select your profile in the "My Xbox" menu, next to the "Play Game" option.
Select "Customize Avatar."
Select "Change My Features." From this menu, you can change the physical features of your avatar, such as the body shape, hair, height skin color and facial attributes. Choose the options that are the closest match for your own physical features.
Select "Change My Style." From this menu, change your avatar's clothing, such as her shirt, pants, shoes or hat. Choose any clothing that most resembles what you would wear.
Select "Marketplace" to buy new clothing options or any licensed products for your avatar. Prices range from 80 Microsoft Points, which is $1, to 400 Microsoft Points, which is $5.
Select "Save and Exit" when finished to save all changes to your avatar.