I searched for some topics about upgrading GPUs in iMacs and I'm pretty confused. First of all can I even upgrade/replace GPU in mid-2010 iMac with HD5750 at all? Or can I have it replaced in Apple Store at reasonable cost? I used to think that GPUs were soldered to motherboard but when I browsed some forums I noticed some people have actually replaced them. I'm thinking about upgrading to 6970 if it's possible. Preferably the 2GB version. Anyone have experience about 5750 to 6970?