You can change your Zune Tag, which you chose when you signed up, by following these steps.

1. Go to Zune.net and sign into your account.
2. Click My Account.
3. Click Change Zune Tag and follow the on-screen instructions. Please note that your account will be charged 800 Microsoft Points.

If you want, you can choose to use your Xbox Gamertag as your Zune Tag.