Build FRF50 was a beta, followed by a second beta FRF72 and now Google has started pushing the final build named FRF83 Over The Air (OTA) a few days back.
If you're running FRF50, you can download the stable update (1.8MB) from Google directly.
As usual, rename the file to update.zip, put it on your sdcard and follow the instructions from #1, skipping #4.
If you have another build, then read on at this link.