You can delete the users from the form by navigating to the Product the School Form is contained in such as onRecord, onBoard etc.
  1. Settings > School Forms
  2. Click Edit on the Form you are looking to remove Users from
  3. Click the Recipients Tab, in User Regarding click the X next to each user
  4. If the form was not submitted or started by the user it will remove them from the Form
  5. If the form has been submitted you will get the message "Wait a minute. This form has already been submitted. Are you really sure you want to remove First Name Last Name as a recipient from School Form Name? If you remove the last recipient it will delete the signed form from  First Name Last Name  This cannot be undone."
  6. If the form has been started you will get the message "Wait a minute. This form has already been submitted. Are you really sure you want to remove First Last as a recipient from First Last name of school form?"
  7. Click Confirm 
  8. After you do this for each user on the form you can now edit or delete the School Form
  9. To delete the School Form click the X