How to change the menu items order?
With the Menu Manager plugin, you can drag and drop menu items to reorder them just like you do with the WordPress menu by default.
Screenshot - 1: (Drag & drop the menu items)
Drag any menu item to the right side, below the parent menu, and then drop it there to create a submenu item. Just like the below screenshot.
Screenshot - 2: (Sub menu items)
As you can see, the Advanced Menu Manager plugin makes it very simple to manage menu item ordering.