@xenial :-
You're talking about reducing the number of virtual desktops, aren't you? You want to go down to just 1, yes?
LXPup, from what I vaguely recall, uses Openbox as the window manager, rather than JWM. So; look for 'Openbox' settings in your Menu - I forget the structure, it's been years since I last used one of these! - then, in the 'Settings' panel itself, there's a bunch of options in the left-side column.
Look for 'Pager' or 'Desktops' - something like that - then set that to 1. 'OK', 'Exit', whatever.....you should then be sorted.
Or do you want to keep multiple desktops, but make it so you have to click on the pager to switch between them? I know how you do this with ROX/JWM, but I don't know how this works with Openbox/PcManFM.
Mike. 