I did that family plan upgrade for one computer and I have decided to
buy a full version of home prem. instead and get a refund from MS for
the family plan key they emailed me.

To activate the new full version can I just go to the activate screen
where there is a button to change the product key instead of upgrading
over my installed version and then activating with the new key? I want
this to be a fresh activation tied to my current hardware since I
already made a hardware change and had to reactivate the old key once
already.