How can I increase VRAM from 128MB to 512MB?

Select the new GMM folder and right-click (or tap and hold) in the right Windows pane. Select New > DWORD (32-bit) Value. Name it DedicatedSegmentSize and give it a (Decimal) value equalling the amount of VRAM you want your GPU to have access to. If you have 4GB of system memory, 512MB would be a good value to opt for.