Instructors can delete a student's post or comment in two different ways.
From the Post or Comment, use the Menu option and select to Delete the Post or Comment
The Post or Comment will still be visible to the Instructor with a note that it was Administratively deleted. Students will not see the post or comments in this state.
Once the Post or Comment is administratively deleted, the Instructor can optionally choose to Permanently Delete it from the topic. The Post or Comment will no longer be visible to the Instructor.
To permanently delete a post that has been administratively deleted, switch from Grid View to List View in order to see the menu icon.