Changing my desktop background?

My daughter loaded a picture(iceberg) from Internet as a background to our desktop computer, due to some reason I can not get rid of the iceberg picture by going to display properties, desktop and "background"(not highlighted) and unable to scroll down and chose (None), Bliss etc.The only option I can use is to chose color and apply which makes the small monitor color to change but nothing happens to the main desktop background(still iceberg).
Has the source of the picture on the Internet locked or disabled my computer?How can I able the "Background" again?