How do i get a new video card for my mac laptop?

I have bought sims 3 but my video card is not up to date with what is required for the game. Can i download the update? if not where can i buy a new video card? can i even buy a new video card? if so how can i install it or who will install it for me? O i have a macbook and the card is intel gma 950|||You can't do anything about it.