How do I delete, change or add multi Storyboards per shot?

On Mobile, open the shot settings, then touch Change Storyboard. From there you can delete or replace the image. 

Use the + option to add additional Storyboards to each shot.

On macOS, right click on the storyboard to delete it: press and hold the Control key while you click on the storyboard using your mouse or trackpad). From there you can add a new one if you need to update it.  

To add multiple storyboards per shot on macOS, open the first storyboard so you are in Gallery view, then use Control /click with your mouse or trackpad and select the Add Storyboard Before or Add Storyboard after option.