You have to get the Administrators Rights to change your account from Utilisator to Administrator. So you need to go the Admin account on the computer (teachers' account) and make the student account admin. Teachers won't notice anything about your account type change but maybe they will see that you used their account.
But, I just have a question for you about that. If you can use the teacher account to change your account type, why don't you just use the teacher account itself ?