I think you are asking how to set the size of the virtual memory. If this is correct then:
1. Open System in Control Panel.
2. On the Advanced tab, under Performance, click Settings.
3. On the Advanced tab, under Virtual memory, click Change.
4. Under Drive [Volume Label], click the drive that contains the paging file you want to change.
5. Under Paging file size for selected drive, click Custom size, and type a new paging file size in megabytes in the Initial size (MB) or Maximum size (MB) box, and then click Set.
Reboot the computer and you are done.