I don't know of any program for underwater car loans similar to those for underwater home loans. (Among other considerations, cars depreciate so rapidly that it is expected they may be underwater in short order.) I gather you don't have friends or family who can act as lenders.
All I can think of is going back to the same dealership to find out whether you can trade up. However, that approach may well take you out of the proverbial frying pan and put you into the fire.
This information does not constitute legal advice and does not establish an attorney-client relationship.