If you have a subscription already, you can't change the LiveID for the subscription.
What happens when you try to install? What errors are you encountering, if any?
See this post for the KB article to troubleshoot install problems - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=1588602&SiteID=2
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
-steve