How can I access my desktop options in Properties/Display?

I am the second owner of this computer and the previous owner was using one of her own pictures as a desktop background. I can change this as often as I’d like using my own pictures, but I can’t access the Windows pictures, or even the stretch, tile, or center option. I can change the color but I can’t see what difference it makes anyway. Is there something that I can do to rectify this problem. Just in case it matters…I am not having the same problem with the screensaver options.

As always, thanks! :)