Saturating your motherboard with RAM sticks isn't the best upgrade for gaming ...
You can't download more RAM, but you can increase how much is available.
I've got a Gigabyte P35 motherboard with 4 ram slots. I used to have 1x2GB stick, but recently bought two more, for a total of 6GB (3x2GB). All are of same kind and speed, DDR2 800. Processor is Intel ...