Microsoft is offering several options for those who want to move from the beta version of Windows 7 to the release candidate when it comes out sometime in the following weeks. Unfortunately, none of them are as easy as a direct upgrade path from the beta build to the RC but rather require a fair amount of work. The recommended approach, according to them, is to go back to Windows Vista and upgrade from that.
The reason offered by the software giant is that they need to get more feedback on the experience that the typical user will have in going from Vista to Windows 7. Those who still want to upgrade directly from the beta will be able to do so, but only using a makeshift workaround of sorts that consists of seven steps to avoid version checking. The steps are listed in Microsoft's blog here. However, the company cautions that going this route might result in "some oddities" after the upgrade so you should try this at your own risk. Alternatively, users can perform a clean install onto a separate partition and use the Windows Easy Transfer feature to move accounts, files and settings - which is probably the best way to go anyway.