You can do it manually. You simply need to create a new project, which will be created with Classic navigation by default. However, you can change it from the project settings once it has been created.
Here’s how to do it step by step:
Create a new course.
Open the existing course and, from the left-hand panel, go to Settings.
There, you will be able to choose between Classic or Vertical navigation.
If you would like to learn more about these navigation types, you can check this article: Navigation Mode.