Hey - just my blow by blow :

Register at the site first.

Then, the serial number you put in to get the upgrade price is the one on file at NI "your registrations and serial numbers" area. Your old serial number.

When I downloaded the upgrade I also received the old KP2 Installer with the new GPO 4 - which I lamely tried to install again and again, thinking it was the installer for GPO 4. Just look in the GPO 4 folder - the correct installer is there. Throw the other one out!

After I installed GPO w ARIA, I tried to drag and drop the activation card onto the opened ARIA app with no success, either as a Standalone or as a plug in within DP.

What I finally did was download the actual file, and take that physically out of my downloads and drop it onto the ARIA player, after which my player was successfully activated.

I know this may be old news because I took so long to upgrade but there you go.

Back to work.