Customize the wallpaper on your Mac
You can change the picture that’s displayed on your desktop. Choose from a variety of pictures or colors provided by Apple, or use your own images.
Tip: You can drag an image from your desktop or a folder onto the thumbnail of the current wallpaper to use the image as your wallpaper.
On your Mac, choose Apple menu
in the sidebar. (You may need to scroll down.)Select a wallpaper from one of the available categories:
Add Photo/Add Folder or Album: Controls to choose your own images.
Dynamic Wallpapers: These images brighten and darken, based on the time of day for your current location.
Landscape, Cityscape, Underwater, and Earth aerials: These still images show dramatic views.
Shuffle Aerials: These still images change at an interval you set.
Pictures: These still images show creative pictures.
Colors: These swatches apply a solid-color background for your desktop.
Set options for your wallpaper.
Options vary based on the wallpaper you choose. For example, you can:
Turn on a slow-motion aerial as a screen saver, using the still aerial of your wallpaper.
Choose how often to shuffle through aerials.
Choose light or dark still versions of Dynamic Wallpaper.
Add your own color.
Tip: You can drag an image from your desktop or a folder onto the thumbnail at the top of Wallpaper settings to use the image as your wallpaper.
To quickly use a photo you have in the Photos app, open Photos, select the photo, click the Share button 
in the Photos toolbar, then choose Set Wallpaper.
You can also use a picture you find on the web as your wallpaper. Control-click the image in the browser window, then select Use Image as Desktop Picture.