This tutorial provides the steps for changing the desktop background in Mac OS X Lion. You can change the desktop background using the option provided as part of System Preferences.
Click Apple menu and select System Preferences from the menu list.
In the System Preferences window, navigate to Personal section and click the Desktop and Screen Saver menu option.
Now you can select your preferred desktop background from Apple, iPhoto or Folders section.
You can also change desktop background after the specified time by marking the check box with label as Change Picture and selecting the required time interval.
If you want quickly change desktop background then right click on the desktop and select Change Desktop Background menu option.