I would like to upgrade from business to 1st on just one leg of a 1st class award ticket (if and when 1st comes available on LH). I am confused about whether any fees should be charged for this. A month ago I upgraded from economy to business on one of the other legs on this ticket that came available. At that time the first United agent said it would be $75 to make the change and I declined and called back. Second agent made the change without charging any fee. Now I am within 21 days of departure, but I am not sure that makes any difference for this kind of change. Anyone know the definitive answer?