First of all, make sure you are in the green Teachers tab of the Admin Hub:
Select the row you want and click 'View user'.
You can then edit the teacher record.
If your edits include a change to the email address for that account, an email will be sent to the new address and the change won't be made until the user clicks on the generated link within that email to verify the change.
Once you have finished editing the teacher account, click OK to ensure your changes are updated.