Is it necessary to remove the trial download version of Windows Live One Care in order to load the retail package of Windows Live One Care, or can one just use the product key from the retail package to activate the already downloaded trail version of Windows Live One care that a subscription has not been purchased for?
Open an installed trial copy of OneCare, click Subscribe, login with your LiveID and select the option to activate your subscription with a retail PIN or key. So, no, you do not need to uninstall/reinstall and yes, a retail key can be used to activate a new subscription. A retail key can also be used to renew without reinstalling. -steveMicrosoft MVP Windows Live / Windows Live OneCare Forum Moderator