First thing to do is download the manual if you don't already have one:
https://www.ipdb.org/search.pl?any=lethal+weapon&search=Search+Database&searchtype=quick#1433
Under AD07 (adjustment #7), you can do all settings at once. Some settings can be done individually, not sure which or if some settings can't be done individually.
Under AD50, when you are cycling through the available options, does it only say the numbers, 0,1,2,3,4? Or does it say Extra Easy, Easy, Factory, Hard, Extra Hard? I would guess that you do have the five options, it's just that choosing "0" is the first option, choosing "1" is the second, and so on.
What version of the game software do you have by the way? It should show you that when you either power the game on or access the settings menu.