I think, default menu (pages) is appearing in the Primary menu location. You have not assigned any Custom Menu to the theme Primary Menu location.
Please follow the simple steps,
– Go to `Appearance > Menus`
– Click on `create a new menu.`
– Give a name to Menu like `Primary Menu`
– Click on `Create Menu`
– Now add some pages or custom links to this newly created Menu.
– Check `Primary Menu` location in `Menu Settings` under Theme Locations
– Save Menu
You are done. Now, you can alter menu items according to your choice.