Product key determines the edition of the installation (developer edition, enterprise edition etc.) RTM is the version number. Since you have already installed the RTM version,, you can install the service packs to bring it up to the latest version. Take a look at this page: http://support.microsoft.com/kb/321185 in the section SQL Server 2008 R2 version information. You can download SP2 from Microsoft http://www.microsoft.com/en-us/download/details.aspx?id=30437