dedicated ram is a terminology mostly used on computers using the onboard video card, dedicated memory is usually around to 128MB to 1GBin most cases, so having 4, 8,or 16GB of ram in your computer will not increase the quantity of SDRAM that you dedicate to use as Video Ram.
if the PC your use is a Desktop, the only way is to install a new video card into your system and use that,
if your system is a Laptop sorry... there is no "upgrade" for laptops worth the trouble (yes there are external video card installations got SOME laptops but 90% cannot use them anyways and most of those installations are worth more than the laptop its being installed on .