Vista Grace/Eval period expired, now to upgrade to higher Vista

Hi. I'll try to explain this as easily as I can

1) I had a computer with Windows XP Professional installed.

2) Windows Vista Home Premium 64-bit that was installed as an upgrade 30 days ago. As you probably know, Vista has a 30 day evaluation or grace period where it can be used without a product key. That's what I did. Now that the period has expired, I want to buy the Vista Ultimate 64-bit RED upgrade.

3) The RED version just makes a donation to a charity and has some extra desktop wallpapers, etc. as far as I can tell. My question isn't regarding that-- you can assume for the purpose of this post that I just said Vista Ultimate 64-bit upgrade.

4) Now, finally, my question: since I already have 64-bit version of Vista on the PC, I can upgrade to Ultimate without a clean install, right?

I would think that the setup DVD for Ultimate would just install the content not already there and the fact that it's already 64-bit means it shouldn't require me to backup everything and do a fresh start, but I'm asking to be sure. Any help is greatly appreciated. I did some searching on Microsoft support articles to no avail. Thanks!!

 

Anyone? For clarity, I should've omitted the entire part about it being the RED edition-- that's irrelevant. Question still stands though