Desktop Christmas Tree Delete Computer Wallpaper PLEASE HELP!?

Computer wallpaper PLEASE HELP!? - desktop christmas tree delete

to learn how to upload your own photos and configure it as a background image? so I've downloaded a few photos on my desk, and I want to delete from my wallpaper too. For example, a picture of the Christmas tree for an option such as wallpaper, but do not know how to delete this option, because it is old. PLEASE HELP ME! Please and Thank You!