MSDN subscription customers can download from the MSDN subscriber download site

Jeff Beehler posted these instructions to upgrade from Beta3/Refresh:

1. Backup your server and copy the data to a safe location
2. Download the Team Foundation Server RC
3. Download the Upgrade Utility
4. Uninstall Team Foundation Server Beta 3 Refresh
5. Follow the upgrade instructions, which are included with the Upgrade Utility
6. Install Team Foundation Server RC
7. Complete the post install upgrade instructions, which are included with the Upgrade Utility

For a reference to the major changes since Beta3 refresh, please see Jeff's posting.