Go to Settings > Desktop and Wallpaper > Wallpaper.

Select a picture.

Select as needed:

Blur: Blur the wallpaper. Slide the slider to adjust the blur level.

Scroll: Let the wallpaper slide with the screen.

Click and select Lock the screen on the desktop.

Set the photos in the photo gallery as wallpaper.

Enter the gallery and find your favorite picture.

Click > set as > wallpaper, and complete the setting according to the on-screen prompts.