Most often you'll set the menu structure up when you create a new page, but in the event where you want to disable or reorder the menu, follow these steps:
- From the admin toolbar hover over Structure > Menus > Main Navigation
- To reorder links, grab the little crossbar icon next to the menu link and drag the menu link to where you want it in the navigation.
- To disable a menu link, uncheck the Enabled check box next to the link.