See post #2 in this thread for link to download site and login info.
Click "mygig software update"
Click "Software - Gracenotes update"
Click "RHR-RHW-RHP 2011+"
Click "RHR 2.126.ISO" to download the 2.126 update for your RHR
It's a big file, so you'll need some good interwebs.
Extract the files, burn as an image to dvd. Insert the dvd into your RHR unit and follow the prompts.
, while not specific to the 2.126 update, has all the information you need to install should you need more information. Just have to read through it.