How to Upgrade/Replace GPU Graphics Card on Mid-2011 21.5" iMac - YouTube
Amazon.com: 2GB Graphics Video Card Upgrade for Apple iMac Mid-2011 27 Inch Core i5 MC814LL/A MC814 A1312 Desktop All-in-One PC, AMD Mobility Radeon HD 6970M Replacement Repair Parts : Electronics
2010 iMac GPU Upgrade to NVIDIA GTX 765M - YouTube