Anyone with Super Admin or District Super Admin access can change the access level of a staff account or delete the account.
Select Settings > Staff to view a list of all of the users at your school or district, broken down by current access level.
Click the settings icon to the right of a user's email address to edit their account. Select "Change Role" to set their new role using a drop-down menu. If you select "No Access", they will be removed from ST Math.
Removing access to an educator's account where they are tied to a class, will have an Inactive label next to their name.
If your district uses a rostering system to manage accounts, you can set the account to be managed 'Manually'. This will prevent any changes you make from being overridden by your rostering system.
If you need to restore access to a teacher you've removed, just use the 'Add' button add them back in! (How do I add new staff accounts?)
See also: What are the different access levels for staff accounts?