Menu Navigation Customization

In my menu navigation I have a few that have subcategories, and a few that do not.

For the ones with subcategories, how do I remove the option of clicking on the parent level page. For example. If I have a page called “States” and list “Arizona,” “Alaska,” “Arkansas” to show up beneath it, I would not want the site user to be able to click on “States” and open up a page. I only want them to be able to click on one on the states.

Any ideas for how I make this change? Thanks!