Sometimes your iDevice needs to be reset to resolve issues with apps running on the device. Apps crashing and other unexpected behavior may be indicators that it’s time to reset your device.
Reset the iPhone by holding the sleep/wake button at the top right of the device and the home button at the bottom center of the face at the same time.
Hold them both until you see the screen go black. In some cases, you may need to keep holding them even after the red power off slider appears. If it does, just keep holding it.
Wait until the white Apple logo appears. When this happens, you can let go – the iPhone is rebooting.