If your computer's operating system is Windows XP or an earlier version, to switch Windows you can use Alt and Tab. Hold the Alt key and press Tab. The screen will display a window with all the open Windows. Continue holding Alt and press Tab to select the desired window. Release the keys to the active window.
If your computer has Windows Vista or 7, you can also use Alt and Tab. The list of Windows will be presented not with icons as in previous versions of the operating system and small Windows. But there is another option. Hold down the Windows key (Windows logo), press the Tab key. Open Windows will appear on the screen in three dimensions. Press Tab or scroll the mouse wheel to select the desired window.