Instructions
Turn on the console and sign in to the Xbox Live gamertag you want to change.
Go to the ̶0;My Xbox̶1; section of the dashboard and highlight your avatar, then press the ̶0;A̶1; button.
Select ̶0;Account Management̶1; and press ̶0;A,̶1; then select ̶0;Manage Account̶1; and press ̶0;A.̶1; This loads the ̶0;Your Information̶1; tab.
Highlight ̶0;Windows Live ID̶1; and press the ̶0;A̶1; button. This opens the ̶0;Windows Live ID̶1; tab.
Select ̶0;Change Password̶1; and press ̶0;A.̶1; This opens a Change Password window.
Input your current password in the ̶0;Current Password̶1; field, then enter the new password in the ̶0;New Password̶1; and ̶0;Reenter Password̶1; fields.
Highlight ̶0;Change Now̶1; and press ̶0;A.̶1; Your gamertag password is changed.