Mac book pro mid 2012 vram

VRAM doesn't affect game performance. It only affects quality and what kind of settings you can run. You won't get any more fps from more VRAM.
If you don't get good fps already, you should get a different computer to play that game.

That being said, Shogun 2 is a Windows game so it really doesn't matter what OSX shows as VRAM. The HD 4000 is an integrated GPU which simply takes as much memory from the system as it needs. Usually a minimum of 64MB and up to 1.7GB under Windows. I doubt that most games will run at settings that need any more than 256MB. Maybe 384 in rare cases.
Anyway the driver in Windows manages that and what Shogun says doesn't matter. I would assume all it says is how much memory the current settings are using.
Use GPU-Z to read out the video memory stats during gaming to see what it actually is using.

 

You can play with higher quality textures at the same FPS. That's the only difference.

Textures are the visual "surface" of every object in a game.

If you're playing in windows, though, it handles vram differently for intel integrated cards and doesn't have an artificial limit like in OSX.

 

is there anyone who succeeded in 768mb of ram?