Product Key question

Here is a possibly unusual question:

 

I downloaded a free trial of norton Internet security 2012 about 2 weeks ago. I liked it! I was at costco and saw that there was a special for a 3 computers Norotn Internet Security and I though that would be great for the desktop pc, my wife's laptop and my laptop. Here is the qeustion:

 

Do I need to uninstal the trial software and then install the software I purchased? or can I just use the prodcut key that came with my purchased product?