You can't. The dedicated memory is what is physically available to your video card/GPU. The rest is virtual memory.
BTW, is this integrated video on the motherboard itself? If so, you can possibly go into your BIOS and raise the dedicated memory to as high as 256MB. Depends on your particular motherboard. Keep in mind that if you do this, adding GPU memory will reduce the overall memory available to your overall system.
Good luck!