How to Upgrade/Replace GPU Graphics Card on Mid-2011 21.5" iMac - YouTube
For iMac 21.5" A1311 Mid/Late 2011 6770 AMD upgrade Nvidia K610m 1GB Video Card | eBay
Upgrading the graphics in our 2011 iMac (first attempt) - YouTube
2GB Graphics Video Card HD6970M Replacement, for iMac Mid-2011 27 Inch A1312 Desktop PC Computer Core i5 MAC814LL/A MC814, AMD Mobility Radeon HD 6970M GPU Upgrade MXM Board Repair Parts
2 GB Graphics Video Card GPU Upgrade Replacement for Apple iMac Mid-2011 A1312 27 Inch Core i7 3.4 i5 3.1 Desktop Computer, New AMD Radeon HD 6970M HD6970M 2GB MXM Board Repair Parts
Upgrade 24” iMac video card - ATI Radeon 256MB to NVIDIA GeForce 512MB - Ask Different
Original Graphics Video Card GPU Upgrade Replacement for Apple iMac 21.5 Inch Late 2011 Core i3 3.1 All-in-One Desktop PC MC978LL/A, AMD ATI Mobility Radeon HD 6750M, MXM VGA Board Repair Parts