You have two choices. Contact support for help in getting the password reset -
How to reach support (FAQ) - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
Or, let the current subscription expire. When it expires, uninstall OneCare, How to Uninstall Windows Live OneCare, and the install the trial from http://onecare.live.com and click subscribe after it is installed and running. Then subscribe with a new LiveID (you logged in with a LiveID to get here to post) and provide payment information or use a retail key from a new retail boxed copy of OneCare.
-steve
Microsoft MVP Windows Live / Windows Live OneCare & Live Mesh Forum Moderator