it's also worth opening up the bottom memory cover and seeing if you have 2 256mb sticks or a single 512 stick ...  if you have 2 sticks currently, you're going to have to remove ram before you add more

 

also, don't expect significant gaming improvements from a ram increase if you already have 512

You can upgrade the memory depending on how many sticks you have already in the system. And I agree with the person before me, adding more memory won't improve gaming. You'll need a better video card, which is very costly or probably impossible to uprade on a laptop.