How do I put in the product key into a trial version

I probably didn't do this the best way, but I had to redo my hard drive.  I have my product Key but I can't find my CD.  So I down loaded the 90day trial version thinking that somewhere I would be able to just type in my product key and be legit.  Only thing is I can't find where to type it in, any ideas.

 

Figured it out: click subscribe... BINGO