There is really no way to upgrade the graphics card unless you replace the whole logic board with a newer one. The graphics cards in Apple's laptops are soldered onto the logic board and therefore can only be removed with special equipment. I would say to just buy a new MacBook Pro and sell the older on to put towards the newer one. There may be ways to put newer logic board in as all the 15" MacBook Pros share the same model number but some one else would have to confirm this. This process would also be fairly expensive as the logic boards can cost upwards of $800.
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