You just can't change your password. If you want to change it, you go tell your teacher your new password, and then when they update grades, that's the password

You just can't change your password. If you want to change it, you go tell your teacher your new password, and then when they update grades, that's the password that will work. Of course, each set of grades is managed by each teacher individually, so you would have to individually update your password on each "system"...