To edit the menu at the top of the page, go in the admin panel, click Appearances > Menus
Using the Add menu items section on the left, you can search for posts or pages to add to the menu
Use the Custom Links to enter hand-written links
The label of menu links can be changed here
Drag and drop menu items to re-organize the menu. Indenting a menu item makes it a sub-item.
When you are done editing, remember to click Save Menu