1. Go to the Staff tab on your dashboard

2. Find the person you want to remove admin rights from (using the search bar if you want), then choose View profile from the three dot menu next to their name

 

3. Select Manage account and then Remove admin rights

 

This person will still be a teacher in your school account. They will receive an email to inform them that they no longer have admin rights.

To remove the staff member completely, read: How can I remove teachers or administrators from my school account?