After updating your Motorola Atrix 4G you will lose root access. Some of you may not care because you only had it rooted for sideloading. For the others if you want to root your Motorola Atrix 4G after updating to Gingerbread 2.3.6 (System Version 4.5.91 & 4.5.141) this is how you do it.
Instructions to Root Atrix 4G running Gingerbread:
1. Download and Extract Fastboot Files to your C: drive [Download Link].
2. Connect your phone to the computer via USB and activate USB debugging (Settings >Applications > Development > USB debugging).
3. Put your phone in fastboot mode (restart phone holding volume down button and push the volume up button when you see fastboot mode).
4. Open a command prompt and navigate to C:/moto-fastboot-win32.
5. Type “moto-fastboot.exe flash preinstall preinstall.img” and press enter.
6. Type “moto-fastboot.exe reboot” and press enter (Your phone should reboot, wait for it to come back up).
7. Type “adb shell” and press enter (to restart the shell)
8. Type “/preinstall/dosu” and press enter
9. If step 8 fails type “/reinstall/su” instead and hit enter
10. Type “/bin/mount -o remount,rw /system” and press enter
11. Type “cp /preinstall/su /system/bin/” and press enter
12. Type “chmod 6755 /system/bin/su” and press enter
13. Type “PATH=/system/bin:$PATH pm install /preinstall/Superuser.apk” and press enter
14. Reboot your phone
Congrats you now have a rooted Motorola Atrix 4G running Gingerbread 2.3.6 (System Version 4.5.91 or 4.5.141). If you want to enable the Hotspot option on your Rooted Motorola Atrix 4G check our post about how to Enable Tethering on Motorola Atrix 4G after 4.5.91 & 4.5.141 Update.