Open the Settings app
Tap Wallpaper
Tap Add New Wallpaper or Choose a New Wallpaper
Select a wallpaper from Photos, People, Photo Shuffle, Emoji, Weather, Astronomy, or a preset collection
Adjust the image by moving or pinching it
Tap Add
Choose Set as Wallpaper Pair, Set as Home Screen, or Set as Lock Screen
If using a photo, open Photos, select the image, tap Share, then tap Use as Wallpaper
On the Lock Screen, touch and hold the screen, then tap Customize or the plus button
Tap the wallpaper preview to change it
Tap Done to save changes