Upgrade help

Hi, I would like some help with my security for my computers.

 

I have NIS 2007 for my system, which was only a 90 day free trial version I got with this PC earlier this year. It recentley expired but when I go to renew, It only gives me the option for 1 user PC license, but now I have 2 PC's so I would like a 3 PC license. My question is this; Do I have to buy a full retail, full priced version of NIS 2009 3 PC license; or could I just buy an upgrade pack with a 3 PC license which is cheaper having gone on the web and seeing them for a much cheaper price on different websites.

 

Thanks in advance.