Can I give more memory to a dedicated video card?

If you were to allow more memory from your ram to be used with your dedicated video card. such as going for 512mb to 1gb. By using my system ram, would that be possible with a m3n78-vm motherboard?|||all modern graphics cards that have a dedicated portion also take from system ram so all possible ram will be being used allready-the only other option is pysical upgrade