Go to Settings → Administrators and click the person. Click Edit to change their permissions, or Remove to take away their admin access. You need the Administrators permission to do this.
Edit an administrator's permissions
Go to Settings → Administrators.
Click the administrator.
Click Edit.
Tick or untick permissions.
Click Save.
Remove an administrator
Go to Settings → Administrators.
Click the administrator.
Click Remove.
Confirm that you want to remove them.
Good to know
The list shows each administrator's name, email, how many permissions they have out of the total and the date they were added.
An administrator must keep at least one permission. To take away all access, remove them instead.
For company administrators, do the same at company level: open the company from the Dashboard, then go to Settings → Administrators.