Yes, adding RAM will improve your performance, but like what sylvia said, contact your manufacturer for more information.
However, you may still not be able to play certain games. Intel HD Graphics comes with ~384 MB of VRAM (?). You can still play games that require 384 VRAM or less, like Call of Duty: Modern Warfare 3, but you can't play games that require 384 VRAM or more, like Battlefield 3.