Things You'll Need
Instructions
Turn on your Xbox 360 and wait for the opening menu (the dashboard) to load. When it has finished, scroll up to "My Xbox"; you can access a new set of options by moving right or left with the left stick or directional pad. Select the second option reading "Sign in" with the A button.
Choose the profile you wish to customize or, if you have no profiles, select the second from last option that reads "Create Profile" using A to confirm your choice. If you are creating a new profile, you will be asked to type in your name (or gamertag).
When you have signed in, return to the "My Xbox" list. Your profile details will have replaced the "Sign In" option from before. With A, select your profile's information to customize your data. A new menu will pop up; select the option to "Customize Avatar." If you're creating a profile from scratch, you will automatically be brought to the customization menu.
You may now begin changing the appearance of your avatars. The top option, "Change My Features," alters the height and facial structure of your Xbox avatar while the "Change My Style" option below it changes the avatar's clothing. Using these two menus, you can select how your avatar will look. When you are finished, go to the main menu and select "Save and Exit" at the bottom.
To further customize your avatar, you can unlock different items through the other options in the main menu. The "Marketplace" option allows you to get additional clothing items with Microsoft Points (purchased with a valid credit card). The "Awards" option is a list of avatar items that must be unlocked by playing certain Xbox 360 games.