To switch your menu into vertical mode, visit the UberMenu Control Panel > Basic Configuration, and set the Orientation to Vertical.
If you are using a Vertical menu, you will likely want to set the mega submenu width under Basic Configuration > Vertical Menu Sizing. Otherwise, your submenu’s width will be limited by the width of the menu bar – which is naturally narrower in a vertical state.
To size each submenu individually, you’ll need to write custom CSS for each submenu. See How to Style One or More Menu Items (or Submenus) Differently