A metro app runs in one of three possible states, active, suspend, or performing some defined background activity like the Mail app. When an app is not on the screen, it’s either off or suspended in the background waiting to be waken up but will be forced to shut down if the system determines that more resources are needed.
So basically, you don’t need to worry about closing down the running Metro app. Simply press the Windows button to switch to Start Screen or go to the Switch menu to switch to another running app.
But if you insist, here are the easiest ways to completely shut down the full screen running app.
The easiest way is to use the old fashion Alt+F4. Once pressed, the current running app will be terminated immediately.
Hold the top edge of the app and drag down to the bottom edge. It’s more like throwing the app to the bottom ground.
You can use your mouse to close the background app from the Switch Menu. Simply right click the app and click Close.
Use Touch Screen
Swipe your finger from the top bar to the bottom, much like using the Mouse, but be patient and swipe a bit slowly than usual.
Use Task Manager
It’s not the most efficient but certainly most powerful way to shut down an app. It’s guaranteed that an app will be closed completely.
Press Alt+Shift+Esc to bring up the Task Manager, find and select the app, and click End Task.