Before you do this, please make sure you know what you are doing. This could end up bricking your device. Believe me, I've bricked an Atrix before.
To get the update on your device, you will have to have the bootloader unlocked, which can be explained here.
- Grab the .zip from here. (EDIT: So the .zip has been pulled from here. Use this instead.)
- Make sure you have the Motorola drivers and the Moto-Fastboot.exe. Make sure the leak .zip is in the same directory as the fastboot.exe.
- Reboot into CWM.
- Wipe data and cache.
- Reboot into fastboot and connect to computer via USB.
- Open up a command prompt on your computer and navigate to the directory where the leak and fastboot are located.
- Execute these commands:
moto-fastboot.exe flash boot boot.img
moto-fastboot.exe flash preinstall preinstall.img
moto-fastboot.exe flash radio radio.img
moto-fastboot.exe flash system system.img
moto-fastboot.exe flash webtop vendor.img
Your Atrix will reboot and then you will have Ice Cream Sandwich!
If you don't have time to use the fastboot commands right now, another developer has thrown together an update .zip that you can flash in CWM. Check that out here, if you are interested.
So does this mean Motorola is still working on an official ICS build for the Atrix? I doubt it. Apparently this build is dated in August, which was before they said they would not be updating it. Hopefully they are, but I don't think we will be seeing anything official. I'm sure the community will be able to make something out of this leak. Follow the thread over at XDA for updates. If you successfully install it, let us know how it is! (EDIT: Motorola has actually stated that the Atrix will not get an update. My bad.)
Shout out to Android Police for the install instructions.
Screenshot picture taken from upndwn4par.