Can I upgrade from a prerelease version of ConfigMgr 2012 to the Released to Manufacturing (RTM) version?
No. You need to bear in mind that as Microsoft have developed ConfigMgr, significant changes have occurred between the various development phases such as Beta 1, Beta 2, Release Candidate, etc. It is therefore not supported for you to upgrade from one of these prerelease versions to the Released to Manufacturing (RTM) version.
This also extends to maintaining data from a previous prerelease version and bringing it into the released version.
Microsoft recommends that you rebuild any machines (including the operating system), on any machines you have installed a prerelease version of ConfigMgr 2012 on if you plan on re-using the hardware for the released version of the product.