First, you need to ask, is my laptop's graphics card actually upgradeable? In most cases, the answer will be a resounding "no". Even if the card is technically removable, almost no one sells the actual cards alone, and where they do, they're very expensive and won't necessarily fit the laptop's cooling solution.
Also, I think you are quite mistaken on a measure of graphics card power: even if you upgrade to the best laptop graphics chip available, you probably won't even use more than 1GB of the graphics memory. Just getting a card for that extra 2GB is almost certainly a huge waste.