If you want to create a menu or change the menu imported by the demo, you can do so. To do this,

follow the next steps:

1. Log in as admin

2. In the left panel go to Appearance > Menus

3. Here you can change the menus, and also change the menu locations.

More information about using WordPress Menus can be read in the Codex, here:

https://codex.WordPress.org/WordPress_Menu_User_Guide