How do i change the amount of my video card being used?

Well my video/Graphics card or whatever is 2GB in memory, and when i play a game such as GTA 4 it shows down the buttom of my GRAPHICS tab that i have ###/256Mb why is that? i want more of my video card used, so how can i do that? if im wrong what is the 256Mb???|||You can check how much dedicated graphics memory really is on your card with GPUZ;

http://www.techpowerup.com/downloads/Sys…



Your graphics card may just have Turbocache or Hypermemory feature such that graphics memory increases dynamically on demand. The additional memory is shared from system RAM. OR if your computer has large RAM installed, Windows Aero is allocating a large chunk of RAM to graphics such that you are seeing 2GB graphics memory.



GTA 4 is graphics intensive and works well with 512MB or bigger dedicated graphics memory, especially when playing at high resolution.