Only an Administrator can change the status of a user who is a teacher.
To begin, go to the School administration menu (1) and select Users (2). You will see a list of all users in your school. Click on "Teachers" (3) to display a list of your school's teachers. You can sort the teacher by name, email address, or those who joined most recently (A). You can also search for a specific name or email address (B). After you have found the teacher, click on the settings icon (4)
Click the down arrow (5) next to the Teacher option and select "No". Then click "Save". (6)
If the Teacher is also an Administrator, repeat the process with the field below it and lick "Save"
Now your teacher will appear in the list of Students.
Note: If you believe that the teacher will never work for your school again, you can then delete their account. Find the teacher in the list of Students (7), then click on the deletion icon (8).