Swipe up from the bottom and pause to open the Dock
Drag the divider all the way to the left or right edge
Tap the multitasking button at the top of the app and choose Full Screen
Tap and hold the gray multitasking button, then select Full Screen
Go to Settings
Tap Home Screen & Multitasking
Tap Multitasking
Turn off Allow Multiple Apps
Close and reopen the app if split screen remains active