Open the Settings app
Tap Wallpaper
Tap Add New Wallpaper or choose an existing wallpaper
Select a photo, color, or preset
Tap Add
Choose Set as Wallpaper Pair or customize Lock Screen and Home Screen separately
Tap Done
To change the Lock Screen screen saver, press and hold the Lock Screen
Swipe to a different Lock Screen or tap the plus button to create a new one
Tap Customize if you want to edit the current one
Tap Done to save changes