I tried several times to have my flight changed to an earlier one on the same day, and each time, they said I was not able to (without paying price difference), and my only option would be stand-by or same-day confirmed. Well, today I got a call from Delta, telling me my flight is overfull, and would I mind changing to an earlier flight and getting a travel voucher? Um, no, did not mind at all! So, I made money on this deal, lol!