If you want to delete a lesson.
Select the course you'd like to edit.
Click 'Edit Course' to start editing course contents.
Once you've done that you'll arrive at the course creation page which looks like this:
Navigate to the lesson you want to delete.
Sselect the rubbish bin icon.
Once you've done that a popup will appear asking you to confirm the action. If you want to continue then click 'Yes' and your lesson will then be deleted:
Your lesson is now deleted.