velkost virtualnej pamate priamo nastavit nemozes, mozes nastavit len velkost strankovacieho suboru, najlepsie sledovanim hodnoty commit charge peak:

To optimally size your paging file you should start all the applications you run at the same time, load typical data sets, and then note the commit charge peak (or look at this value after a period of time where you know maximum load was attained). Set the paging file minimum to be that value minus the amount of RAM in your system (if the value is negative, pick a minimum size to permit the kind of crash dump you are configured for). If you want to have some breathing room for potentially large commit demands, set the maximum to double that number.

podrobnejsie:
How Big Should I Make the Paging File?
Pushing the Limits of Windows: Virtual Memory