Want to change your desktop background (wallpaper)? That’s to say, the main picture on your PC screen. Go to Start, then Settings and then Personalisation.
In Lock screen, select a picture.
And because it’s Halloween coming up (when this page was originally written), try using these Halloween themed images as your desktop image, or lock screen.
Left click the image, then choose ‘Save image as’, and save it in your chosen place. Then follow the instructions at the top of this page.