On both PIE and cPanel, the Illinois Theme allows you to choose between the default WordPress menu system and a special megamenu.

The default WordPress menu system is the simplest way to create menus; you can choose to automatically add new pages or posts as they’re created, or you can construct your own menu.

From your dashboard, under the Appearance section of the left-side menu, choose the Menus item.

In the Menus page, arrange your pages, posts, and/or categories as you wish.

The Site Navigation checkbox is checked to display your new menu at the top of the page.