First, your virtual memory is composed mainly of your paging file which is hidden on your hard drives and your physical memory installed(Hardware). Now, for us to tweak the virtual memory, we will increase the paging 1.5x the physical memory installed.
So here's how to do it.
Select my computer, right click on it, then go to properties.
Then click the tab advanced, in there you can see under performance, settings.
Select on settings, then you can see another tab advanced.
Select on it once again, and below it says virtual memory, below it, there is the tab change, select change.
Once you're in there, select custom size, then on the initial size, key in the 1.5x your physical memory(currently installed RAM), then copy the same numbers to the maximum size.
Just remember that it is based on MB or megabytes. So for example, if you have 2 gigs of RAM, that is approximately 2048 megs. multiply it by 1.5, you will have a quotient of 3072 megs. Now that is what you will key in for the initial and maximum size.
Therefore, your total virtual memory that will be used by your computer is 5 gigs. So enjoy multitasking...