Graphics Card upgrade

So after successfully running boot camp on my computer, I've discovered that it's not good enough to run any of the games that I wanted to run, so I'm out of options other than buying a whole separate PC which I don't want to do. The main problem with it is its graphics card, as everything else is fairly good. So my question is whether or not it's possible to upgrade the graphics card.

It's an imac model 9,1 with 8 gigs of DDR3 ram, a 2.66 GHz dual core i5 processor, and a nvidia 9400 graphics card. I know it might not be easy, but is there any way that I can upgrade the graphics card? And if so, it would need to be a good one, as I'm looking to run games like Red Orchestra 2 and Arma 2 on high settings, and BF3 and Crysis 2 on medium settings. Thanks.

Not possible without swapping out the entire logic board. The nVidia 9400 GPU is surface mounted to the board along with its VRAM. You can check out what the board looks like by going to the ifixit web site with your model number and view the take apart instructions.