How to maintain PC security whilst installing NIS 2012

Hi, can anyone advise how to best do this? I've NIS 2011, subscription about to expire. I've bought a new NIS 2012 box product, and looking at previous posts I see that I have the option to uninstall 2011 and newly install 2012, also that there is a link to the latest 2012 that I can use the new key with.

 

If I download 2012 then uninstall 2011 will this compromise the PC's security?  Also the box instructions say to close all programs before installing - if I chose the install without removing 2011 route, would I have to close NIS too?

 

What's the best way of achieving the upgrade without compromising security?

 

PC is Acer 5742Z running Windows 7 with latest updates

 

Thanks