64MB Video Ram in Bootcamp?

Why is my Bootcamp's VRAM only 64MB when my Mac states it has 512MB?

On the website 'Can You Run It', this low VRAM is what's making my games fail the recommended.

HERE ARE MY SPECS:

Processor 2.9 GHz Intel Core i7

Memory 8 GB 1600 MHz DDR3

Graphics Intel HD Graphics 4000 512 MB

I can still play games on Bootcamp (Battlefield 3, GTA 4... and even much older games) but they lag upon turning up to even medium settings.

Mac games run perfectly, though.

How do I fix this problem?