To switch your menu into vertical mode, visit the UberMenu Control Panel > Main UberMenu Configuration > Basic Configuration, and set the Orientation to Vertical.
Appearance > UberMenu > Main UberMenu Configuration > Basic Configuration
Vertical menu submenus have a default width of 600px. If you would like to change this, you can do so in the Control Panel. You can also control submenu width on an individual submenu basis with the Submenu Width setting in the Menu Item Settings > Submenu panel.
Note that if you are using multiple UberMenus of different orientations, you’ll need to add an additional Configuration and set the Orientation differently in order to have two UberMenus each with a different orientation.