I take it you are talking about the wallpaper.First we will try to change it like this:-
1)Right click a clear area of your desktop.
2)Highlight active desktop.
3)Click customize my desktop.
4)Click on the background tab.
5)Select a new wallpaper that appears in the select an HTML Document or picture box.
6)Select how you want your image to appear on the screen. Center-Places the image in the centre of the screen , Tile-The image displays as tiles across the entire screen , Stretch-The image covers entire screen.
Also you could read this Microsoft article click here
Also you could try this free tool for tinkering about with your wallpaper and its configuration click here
Hope this is of help to you !