You can adjust the screen reachability for easier one hand mobile phone navigation.
Turn on Reachability
Return to the home screen
Tap the indicator next to "Reachability" until the function is turned on.
Adjust screen reachability
Tap General to save the setting.
Tap the Home key to return to the home screen.
Touch the Home key twice in quick succession and the upper part of the display shifts down.
*Please refer to the Apple website for more information or further support.*