First, you have to make some configurations in the Unity project.
- Switch to Visible Meta Files in Edit → Project Settings → Editor → Version Control Mode
- Switch to Force Text in Edit → Project Settings → Editor → Asset Serialization Mode
- Click on Save Scene and Project from File menu.
- Quit Unity and then you can delete the Library and Temp directory in the project directory. You can delete everything, however keep the Assets and ProjectSettings directory.
Now you have to do the following: