Hi, silverman.Welcome to the forums.
If you wait until a day or so before the subscription expires, the best way is to click on Renew on the UI, and select *I have a key or code to enter.*
I believe you can just enter your key, and you can update your current version subscription keeping your settings, without having to reinstall the multi device version, as it's the same product.
Run Live Update, until advised no more are found.
The single key code lets you activate protection for your other devices.