Hi Zuluking
If you are running build 39979 (the first RC release), then the update is a small 2.9MB file to go up to 40040. Please keep in mind that running a RC release means that you are not running an official release, and as such we cannot offer full support for it. I would recommend that you update to the official SP2 released.
If you are running on build 40040, then you are actually running the official SP2 release.