sounds fairly straight forward to me. what is it that you're not able to figure out? what happens once u follow the instructions and change the wallpaper in settings? does your screen remain black, or does the background not change at all...
if all else fails, try using ifiles and going into the theme's config.jss file and changing the background file source there.
g'luck.
Yes screen stays black.
And I have no idea how to use config.jss. Oh well theme not for me then.
It's difficult to tell exactly what people are or aren't doing but make sure you're setting the Lock Screen (or Both) in the Wallpaper settings.