how i can???? it's impossibile on microsoft site billing!!!!!
To prevent the renewal of OneCare you can invalidate the credit card information by changing the expiration date, but it would be better to contact Customer Service for Billing to cancel the account at the end of your subscription term.
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve