In Windows 8, when you choose or open another application, you can let the last application handled by Windows to be closed, but for better performance if you don't use that app you can close manually.
To Close an application in Windows 8
• Using Mouse :
Move the cursor to the top until the cursor change to
(hand icon), click and drag the application to the bottom of the screen. then App will close.
• If using the touch screen :
Swipe from the top of the screen to grab the application and then drag it down to the bottom of the screen, app will close.
• The classic way is using shortcut Alt F4, press at the same time key Alt+F4 , then Application will close.
See Also :
Change Product Key In MS Office 2010
Solve Problem When Installing BBM for Android
How To Change to other Product Key In Windows 8