There may be some circumstances requiring you to remove a student from a course. Here is how you do that:
Click Students in the side bar.
Locate the student in the list, or search for their name or email address.
Click Show. You will see the courses they are enrolled on.
Click Manage on the course you want to remove them from.
Click the red button Expel From the Course.
You can also block a student from accessing your courses, as explained here: How to Block Student Access.