NIS 2011 to NIS 2012 upgrade ?

I have NIS 2011 on  my PC & want to upgrade to NIS 2012 of which I already purchased a retail boxed version.

If I install 2012 from the disc will it overwrite 2011? Or is it better to upgrade with an online 2012 & then use the 2012 key in order to activate it?

Here’s my concern. My PC came with NIS 2011 & then I purchased a retail version of NIS 2011 in order to extend my subscription. I never installed the purchased version of NIS 2011, I just used the key to extend my subscription. Problem is I have vers 18.6 and LiveUpdate is not updating to vers 18.7. I understand it suppose to, but it’s not happening. This makes me wonder if a retail purchased upgrade is handled differently than an online upgrade.

What’s the best way to handle the upgrade, or does it make any difference?