Windows 10 provides several options to customize the desktop background. Here's how.
1. Open personalization settings
Instead of taking the long way round, i.e. Windows logo > Settings > Personalization (1), right-click the desktop and select "Personalize" (2).
2. Customize background
Click the small arrow (1) to reveal the available background modes (2).
"Picture" allows you to select either from the available pictures (1) or use "Browse" to select a local image (2). "Choose a fit" provides several options that determine how the image will fit your screen (3).
4. Solid color
If you'd rather not use an image but a single color for your background, select "Solid color" (1), followed by the color you'd like (2). If your color is not listed, click "Custom color" to define your own color (3).
Select "Slideshow" (1) to have Windows auto-transition through multiple images. Select "Browse" (2) to choose the folder that holds the images. You'll find additional settings, such as the display duration, at the bottom (3).
Once again, "Choose a fit" determines how the images will fit your screen. "Fill" means the image viewport will auto-adjust to avoid image distortion.