How to: Adjust your desktop background
1 Find your desktops
The second you launch macOS High Sierra, you’ll see it has a brand-new desktop background. If you’re not keen, you can change it. In System Preferences, go to Desktop & Screen Saver. You’ll see High Sierra selected.
2 Change the background
If you fancy using a background from an older version of macOS or OS X, simply click on it. Alternatively, select from Solid Colours for something plainer, or Photos for a custom image from your own collection.
3 Drag and drop
You can also adjust the desktop background by dragging and dropping an image from Finder to the ‘well’ in the System Preferences pane. Fancy shaking things up more often? Tick the Change picture and Random order boxes.