It's pssible but not recommended, there is a workaround on the Microsoft site.
With a new computer instalation should take around 20-25 minutes.
So if you install the version you have and download the new W7RC and install again, that's how much time you will loose.
By the time you fiddle with the workaround and the upgrading is likely to take longer than a new install, is it going to be worth it?
Do yourself a favour and start afresh, knowing you have no old baggage to contend with, what's another 20-25min.