It's very simple and generally speaking the later versions have more compatibility and bugs fixed.
But at this point, you would be well advised to upgrade to the RTM which is v. 7600 since it is pretty widely available already if you know where to look, and in less than 30 days initial grace/trial period, Windows 7 will be launced, i.e., generally available so you have plenty of time to get and add a valid license key, even without using any of the 3 30 days rearms of the grace period that are available to you. So you could use Windows 7 RTM (7600) for 120 days without a license and just get a license before those 120 days are over.
As far as upgrading to the RTM from the RC, it's also very simple, but there is a simple special procedure you must follow outlined by MS at Engineering Windows 7 : Delivering a quality upgrade experience
Most people will advise doing a clean install of the RTM version, however. This is always a good idea, but in many cases the upgrade procedure from the RC to the RTM works pretty well. It might be worth trying and if it works out for you . . . great. If not, you can always clean install again.