Manually removing (unenrolling) Students or Teachers from your Moodle course:
To unenroll someone from one of your courses, you can go to the Participants list (on the Navigation bar).
Once you've found the user on the list of participants, click on the Trashcan icon located on the far right of the list (under the Status column).
If you're a Teacher in the course, be careful not to remove yourself by accident - you'll temporarily lose access to your course.