You can trade it in for a cheaper car and put the remaining balance on the new loan. There is really no way to get out of it, I was in that mess for awhile.
Most lenders will do an 'over advance (110%- to 140%) . So you do not have to trade down to cheaper and often trading up is easier. If you are buying a new car, sometimes the rebates can 'cover' your loss. 110% of a 30, 000. dollar auto is a lot more room than 110% of 10,000.