To edit the Navigation, go to Content > Pages > Navigation
The main site navigation is located in the website's top header and it displays the Parent (or Top Level) navigation items.
Second Level navigation will display in a drop down window called a "mega-nav," whenever a user hovers over a Top Level nav item. In the next section of this guide, we'll take a look at how to manage the pieces of the mega-nav.
Second Level navigation items can have children of their own, but these third level navigation items will not show up in the main navigation or mega-nav—they will, however, be displayed in the sidebar of pages that use the Subpage Default template.
Help Site - Video Tutorial - Adding A Navigation Item