Hey. I have a 21.5" iMac. Here are the specs: Processor: 2.8 GHz Intel Core i7 Memory 8GB 1333 MHz DDR3 Graphics: AMD Radeon HD 6770M 512MB Software: Mac OS X Lion 10.7.5 From the heavy 3D gaming I do and the low FPS I get, I highly doubt it's the processor's fault, I think the measly 512MB graphics card is to blame, and so I'm looking to replace it. However, I really have no idea where to start, so I have a few questions... Does anybody know if I could replace it myself? Where to buy a new one? The cost?