Is this the release candidate? I would not use any version earlier than RTM as there are still bugs, and a ton of bogging monitoring software taken off in the RTM 7600.
You say you found an option to Upgrade but don't mention what you are considering upgrading. It might work but you are "upgrading" to a pre-release beta that was still buggy, slower and not comparable to the polished product Win 7 has become.
I suggest instead you download the 90 day trial of Win7 enterprise from the MS website. I believe you can upgrade to that as well (check back here if you need workarounds) although a clean install is always preferable. There is a way to later upgrade to another version if you decide you want to buy a key to insert after trial.