Mac, is a series of personal computers (PCs) designed, developed, and marketed by Apple Inc. Your Mac comes equipped with more than the default picture.
You can change your background of desktop to follow these below steps-:
1. Go to the Apple menu and choose System Preferences
2. After choose System Preference Click the Desktop & Screen Saver button.
3. Click the Desktop tab; the left pane lists the different folders from which you can choose an image. The right pane displays thumbnails, small images, of the images in the selected folder.
4. After choose your image it will be apply automatically to change desktop images.