Main menu doesn't display sub-categories

At present, from what I can see, site visitors can navigate the main menu bar by only selecting categories. If there are sub-categories assigned to a particular category that the user wants to see, the user must click on the category, which brings up a new page, then select the sub-category. This isn't very user intuitive or visually appealing. Is there a setting buried deep in the back-end or some other alternative that can be integrated to fix this?

Please advise.

Thanks all!

Use some other themes for sub category menus