Here is the link to flash an SBF file, which will do what you're looking for. Choose 4.1.26 if you want to go back and root again or 4.1.57 if you don't want root and don;t need sideloading enabled.
[GUIDE] Flash SBF to Motorola Atrix 4G - xda-developers
If you want to flash back and root, then update while keeping root, see here:
[SCRIPT] GladRoot (Bell 0.37.4, AT&T 1.26/1.52/1.57 Supported) - xda-developers
Good luck!