How do I enter my Product Key for NIS 2011?

I have been using NIS 2010 upgraded to 2011 for a year.  I liked it so much  I just bought a new 1 year program with product key on the auction site.  How do I enter my new product key without reinstalling the NIS 2011 program again?  Do I need to re-install from CD since I upgraded to 2011 about 5 months ago?  Newer code? Thanks