Instructions
Log into your Xbox Live profile and enter the Avatar Editor from the main menu. Click the "Customize Avatar" option from the "My Xbox" menu.
Select the "Change Appearance" button in the Avatar Editor and then the "Ears" tab. Choose the "Spiked" ears for an elven appearance.
Return to the Avatar Editor main menu and enter the "Marketplace." Browse to the "Lifestyle" tab and over to the "Fantasy" collection of Avatar clothing and props. Scroll over to the "Elf Costume" to demo the costume on your Avatar.
Pay 240 Microsoft Points using the credit card associated with your Xbox Live account to download the "Elf Costume."
Enter the "Change My Style" section of the Avatar Editor to dress your Avatar. The "Elf Costume appears in the "Dress Up" area of clothing options. Don't forget to use the "Save and Exit" option to preserve your Avatar's new look.