When you originally setup your Xbox Live account, you had to either create or specify a Windows Live ID account to link to your Xbox Live gamertag. This ID doesn’t necessarily have to be permanent though, you can change the ID that is tied to your gamertag if you need to.
1. Sign into the gamertag that is as associated with your Xbox Live account on your Xbox 360 console.
2. In the My Xbox section, scroll over to Manage Account.
3. On the Account Management menu, select Windows Live ID.
4. Select Change Windows Live ID, and it will prompt you to confirm your selection.
5. Enter the password for the Windows Live ID that is currently associated with your account and select Sign In.
6. Enter the email address and password for your new Windows Live ID and select Sign In.
7. Select Yes, change to confirm your new ID.
