You can change your billing information by signing in at
http://billing.microsoft.com but it is not really necessary since One Care is nearing end of life and renewals and new subscriptions are no longer being accepted. See this post -
http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/0000c782-ed1b-4ed3-8afb-87989bb9638c
Jim
Microsoft MVP Consumer Security - Forum Moderator - Live One Care - Live Mesh - Microsoft Security Essentials