Close some apps in the system tray, or if the risks go, press Ctrl+Alt+Delete to enter the task manager. You can end processes by going to the process tab; though just be sure to know what you're doing there.
Best not to end any system processes generated by the system or any system files (e.g. rundll32.dll). You can safely close applications from there, but the other convienient way is to buy more RAM.
