Dude, take a deep breath.
Go into Settings/Display/Screen. Do you see where you can change the font and homescreen wallpaper? On that same sub-menu there's another area for lockscreen wallpaper. Click it, it'll take you to the wallpaper cropper. Once you've cropped the image in the wallpaper cropper, be sure to hit OK in the upper right of the screen to save and set.
Alternatively, go into Gallery, find a picture you like, open the menu, it'll give you the option to set as either a homescreen or lockscreen wallpaper, then go through the standard crop process.
Lockscreen Wallpaper is NOT handled by the launcher code, it's an OS level action, FYI.