In iOS7, if your app doesn’t respond or if you want to stop an app completely so that it won’t run in the background using device resources, its very easy to force quit an app.
In your iPhone, iPad or iPad mini, double click on home button. The multitasking system will appear, displaying apps icons and relative app screen preview.
To stop or remove the app functioning completely, just swipe the app screen preview up to the top of your screen. Now, your app will not run. You can start it afresh to use again.