Hy SU,
thanks 4 replay. Now I create new menu in Joomla and call 'em Glavni-meni [horizontal-main-menu] then duplicate all menu links from old menu called Top Menu [topmenu] and now Megamenu configuration look like this 'prt scr' (here is picture).
When I first time creating top menu for site which I called Top Menu [topmenu] (megamenu) it's look the same as the new-one and like U can see on this new 'prt scr'
In bot case, old megamenu (befor I switch 'em off) and new-one has the same Frontend 'prt scr' (here is picture).
Anyhow, creating new menu in Joomla automatically putt 'em into Megamenu configuration and now it's working fine, so problem is solved.