1. When viewing the Slide Editor, Click on the icon that has a minus sign within a Slide Navigation item.
2. A confirmation dialog will appear to confirm if you want to delete that slide.
3. When you click okay, the slide will be deleted and will no longer appear in the Slide Editor
Here is a video walk-through on how to do it:
TIP: If you delete all Lesson Slides on the Slide Editor, you can add new ones as you desire.