How do i change my wallpaper ?

Hello,

someone please help me . i try everthing that i had to change mt desktop wallpaper but nothing is works . i already go to contol panel but there are not mention about desktop wallpaper at all . what should i do ? i go to desktop and clicking on right click but there also dont have a properties . u used acer laptop . then i try using clicking on right click with one picture but there also dosent mention about 'set as wallpaper background' . what should i do guys ? im a new user of acer laptop .