Change the desktop and lock screen backgrounds
To change the image used for your backgrounds:
Open the Activities overview and start typing Background.
Click Background to open the panel. The current selections for Background and Lock Screen are shown at the top.
There are two ways to change the image used for your backgrounds:
Click one of the background images which are shipped with the system. You can choose Set Background, Set Lock Screen, or Set Background and Lock Screen.
Some wallpapers change throughout the day. These wallpapers have a small clock icon in the bottom-right corner.
Click Add Picture... to use one of your own photos from your Pictures folder. Most photo management applications store photos there.
The settings are applied immediately.
If you would like to use an image that is not in your Pictures folder, right-click on the image file in Files and select Set as Wallpaper, or open the image file in Image Viewer, click the menu button in the titlebar and select Set as Wallpaper. This will affect only the desktop background.
to view your entire desktop.