Probably not possible. Laptops usually use the dedicated graphics in the CPU (i.e. Intel HD series); since they share memory with the OS, the only way to increase that is to increase the laptop's total RAM...and even then, it still may have a hardcoded upper limit for the video portion.
For the ones that have a discrete "mobility" card inside, "upgrading" the memory works just like with a desktop: you have to replace the entire card. Unfortunately, replacing a graphics card in a laptop is extremely difficult, due to the limited space, problems with disconnecting then reconnecting all of the pieces (keyboard, mouse pad, etc.), & the problem that all too often components like that are soldered or glued into place to preven removal by anyone except authorized repair techs.
Now, what you could always do is contact Gateway to find out if you can have them install the nVidia GT 620M in your laptop (option for that particular model), since it comes with 1GB of dedicated VRAM. If not, you're probably stuck.