Graphics card memory (VRAM) doesn't have as much impact on performance as their marketing teams would like you to think.
The only time more VRAM will help is if you're running out of frame buffer, typically by running at high resolutions, high res textures, or lots of AA.
The GTX 650 is much, much better than your current onboard graphics, the Intel X4500, so will perform much, much better in games.
Remember, each specification on a graphics card - core count, core clock, amount of VRAM, memory bus width, etc - is only part of the bigger picture, so it's impossible to judge performance based on one specification alone. Judging a card based on its memory is what the marketing teams usually want, because it's an easy point of comparison and it's cheap for them to increase the VRAM from, say, 1GB to 4GB and charge extra, increasing their profit, when in reality the card is often too weak to take advantage of the extra 3GB of VRAM, and sometimes the card is even crippled in other ways so it's actually slower.
