Go with 'Pro'
Mate you done exactly what I would have done.
That is a clean install.
I prefer to delete all remnants of older software of my computer before I attempt to install a newer version, incase of conflict. I hate upgrades, adding on wee bits of code here and there when infact you can get it all in one.
You bought the CD of Pro so obviously you will upload the whole CD. You will have to contact 'Zone Labs' if the suppositly obvious answer doesn't work.