As far as I know, and this is pretty much true for most if not all laptops, vram as you put it, the video cards that are supplied onto the laptop are generally not user-serviceable. One, the video card/chip is directly on the motherboard, and chip makers don't often/if ever supply these chips in bulk. You may be able to find one online or at a store like Fry's or something, but .. I don't know if anyone has ever been successful in replacing the video chip for one that is bigger.
I could be wrong, but at least in my experience for other laptops, pc laptops this is true, and I believe this is true for the mac laptops and even the desktops for apple (well besides possibly the mac pro).
