From time to time, apps on your iPhone or iPad can become unresponsive, or behave eratically. Often the fix is to restart that application. To force an App on your iOS device to quit, follow these steps:
1. If you're not already in it, open the App you're having trouble with.
2. Hold down the Power button at the top of the device until the red “Slide to Power Off” message appears and then release the power button.
(Do not slide the slider)
3. Now hold the Home button on the front of the device for a few seconds, until the app forcibly quits. You will be returned to the Home screen.
4. Try launching that application again to see if your problem is resolved.