Your browser stores your log on details not BT.
You need to go to your browser's settings and find the "Stored Password" settings and scroll through the list until you find the ones referring to your BT email log on details. Once you have found it delete it.
The next time you go log on, your browser will offer to save the password details. If you want this click on it to accept it.
The next tile you log on the details should then be entered into the log on box by your browser.
If you have more that one BT email account you will need to do this for each one.
