Ok, I understand better now, I thought you were asking about increasing the on-board video memory which is not possible.
Anyway, if performance is not great, it's unlikely to be due to unsufficient Video memory, but more to non-optimum platform profile settings. I recommend that you read the article about "Performance Tuning with FakeSMC" in the Articles pages of the web site and adjust your laptop's settings accordingly.
I can tell you that I do not experience any particularly poor performance on my D630 nVidia 135M with FakeSMC v5.2.678, SMC id set at 1.33f8 and SMBIOS profile set as MacBook Pro5,1. We tested this profusely a few months ago and reached top optimal performance, including graphics performance.
On 64bit Mavericks 10.9, you may actually use any recent release of Kozlek's FakeSMC kext + HWMonitor app. Be cautious as the downloaded package will install the FakeSMC kext (with plugins inside) in /S/L/E. You need to move that back to /E/E and re-run myFix (full) for the kext to be used subsequently after reboot.