My Mac’s Desktop is usually filled with so many app windows that it’s impossible to see the Desktop image, However, if yours isn’t and you want to change the Desktop picture, it’s easy to do.
But first a reminder: don’t confuse the Finder with the Desktop. The Finder is the first thing that you see when your Mac finishes starting up. It opens automatically and stays open as you use other apps. It includes the Finder menu bar at the top of the screen and the Desktop below that. The Desktop is the space where you see file, folder, and application windows.