This way requires two-button mouse and keyboard. You should be logged in to your Gnome to use this tutorial.

Clicking means always a hit of primary (1st or left) mouse button when the cursor is in the requested target. Usage of secondary (2nd or right) mouse button will be declared when it is required.

The Basic Tutorial

1. Click your current background using the secondary (2nd or right) mouse button. You will get a menu
   
2. Click the entry called ”Change Desktop Background”. ”Appearance Preferences” window with “Background” tab on. Now it's up to you, what you want to do. If you want to use the backgrounds installed with your system:
   
3. Click the thumbnail you want to see on your desktop. You will see the preview on your desktop, behind the window.
   
4. If you want to keep it, click “Close” button. If it is not that you want, you can go back to the step 3 (a or b) and choose again. If you want to use your own image file as your desktop background (experimental):
   
5. Click “Add..” button.
   
6. Select the background image you want to use
   
7. You will see that image previewed on your desktop. 6..If you want to keep it, click “Close” button. If it is not that you want, you can go back to the step 3 (a or b) and choose again. I know, this article can be useless but someone can sort out something or find easier way to change the background image (=wallpaper).