If you are not logged into your mobile account, you will be requested to login with your email address and password.
Remove Billing Account From Mobile Account
Select 'My Bill' from the home or side menu.
Press and hold down the billing account in the list, that you are intending to delete, for approximantly two seconds to three seconds.
A 'Confirmation' prompt will appear asking you to verify that you want to remove this billing account.
Press 'OK', and the selected billing account will be removed from your mobile account.