To remove the second-level drop-down menu or bring the page back to the upper-level submenu, follow these steps:
1. In the Navigation settings menu, grab the hamburger icon on the page you want to relocate and move it into the upper portion of the list so that a line appears inside the upper-level page element:
2. To remove the drop-down menu completely and bring all pages back to the main menu, repeat the step 1 but drop the pages, not inside another page but where a guideline appears:
Your pages will return to the main menu, however, if there's not enough space, they would be automatically moved to the More submenu. Learn more about managing More submenu in this tutorial.