You can see the amount of Virtual memory (or page file) your programs are using with task manager : go to view tab and click select column and click virtual memory and ok. You can close some of your background programs that you don't use which consumes more virtual memory .
Usually the amount of virtual memory is 1,5 x your RAM memory.
And windows increases it automatically when needed. (see the yellow message from the taskbar)
You can increase it by right clicking the my computer icon on desktop and proprieties, go to advanced and settings button in performance.Go to advance and click the change button under virtual memory .
Like I said it's usually 1,5 x your RAM.
You can change those numbers, but try step by step, try just a few MB at first.