You can Load and Unload scenes with without writing a single line of code.

The Load Scene Node and Unload Scene Node will help you do that with ease. Load Scene Node is a specialized node used to load a scene.

Unload Scene Node is a specialized node that tells the SceneDirector to unload a Scene either by scene name or scene build index. This will destroy all GameObjects associated with the given Scene and remove the Scene from the SceneManager.

Besides unloading a Scene, the Unload Scene Node can wait until the target Scene has been unloaded before activating the next node in the Graph.

This Nody tutorial explains how it all works and how to use these nodes.