If you want to delete a question from a Quiz, Test or Poll that you've setup it's easy.
Select the course that you've added the campaign to:
Now the course creation engine has loaded. Navigate to the module you have added the campaign to and select the Quiz icon:
Now your quiz details will appear as well as the questions you've previously added to your Quiz, Test or Poll.
Find the question that you want to delete and then find the 3 dot icon to the top right of it.
After selecting this icon a dropdown menu will appear. Select 'Delete' from within that dropdown menu.
Your question is now deleted. Click 'Save' to confirm your changes and update your test within your course.