you can't increase it, since dedicated memory is a hardware limitation.
you're best off getting a dedicated gaming GPU if you want to play games.
Rightly stated by reiyu. It's probably due to the hardware restriction you have. Could you please list down the complete specs here? This should give some clues with identifying the possible work around. In the meantime you might want to get the drivers updated through : Support for the Mobile Intel® 4 Series Express Chipset Family
Dedicated memory for Intel Graphics isn't hardware limited, it's configurable in the Bios depending on system RAM and Bios. Guild Wars 2 is a really new game, I doubt it will run on the old GMA not matter how much dedicated memory allocated. It needs a HD graphics 3000 at least.