How to Restart Applications for an iPhone
Application hangups on your iPhone can be fixed by restarting them using the multitasking menu. This menu is available for the iPhone 4 and the most recent versions of the device's operating system, which enables easy access to view, close or restart applications in the background. Similar to the customizable home screen, the multitasking menu shakes when in editing mode to allow applications to be closed or removed.
Double-tap the home button on the mobile device.
Hold down your finger against the application's icon in the menu at the bottom of the iPhone screen.
Tap the "minus" icon on the application, and press "Home."
Touch the home screen, and tap the previously closed application's icon to re-launch it.