You can change the background image (wallpaper) that displays on both the iPhone’s Lock screen and Home screen, and it’s very easy to do.
Open the Settings app and tap Wallpaper, followed by Choose a New Wallpaper. Here, you have four options to choose from.
The first three options are for Apple’s default wallpapers. Tap Dynamic to select a wallpaper that animates as you tilt and move your device, or select Live for a wallpaper which you can interact with by touching your device’s screen.
The third option, Stills, includes four wallpapers which subtly change in appearance when your device switches between Light Mode and Dark Mode. There are also a number of standard wallpapers available to choose from here, too.
Below these options, you’ll see albums of images from Photos. Choose an image from your Photos library if you’d like a more personalized wallpaper.
When you’ve chosen a wallpaper, tap Set and select if you want to use this image for the Lock screen, the Home screen, or both.