Through this tweak you can change the appearance of your desktop wallpaper.
1) Display wallpaper as centered.
2) Tile wallpaper until screen is filled.
3) Stretch wallpaper to fit the screen.
For this, go to Start > Run menu, enter “regedit” and navigate to the registry path listed below. Now, check the String values “WallpaperStyle” and “TileWallpaper” and right-click to modify their values as in table below:
The changes take effect after a restart or logoff.