RAM problem !!?!! pls help !!?

i have a pc win 7 32 bit and 4 gb ram. but when i see computer properties i see ram= 4 gb (only 2 gb usable) pls help also i hv i3 and nvidia graphics 512 gb but games like gta4 and ac brotherhood or even capsized work really slow pls help my pc is jst 6 months old !!!(these games worked slow but prototype was just fine !!!) also i want to ask tht though buy games but do orignal work better than pirated or downloaded ?? i am srry but i am short of points !!