The most common misconception about short selling a property, is that anyone can do simply because they owe more than the property is worth. This is not accurate. Before you consider this option, you must first validate that you have an eligible hardship. An eligible hardship may be a qualifying illness and related medical bills, extended loss of employment, and equally important, a delinquincy on your mortgage payments.
Without a qualifying hardship, you will not be allowed by your mortgage holder to sell the property for less than you owe on the mortgage just because you want to or just because it stinks to owe more than the property is worth, unless you agree to pay the difference at closing of the sale.
The link I have included will provide more detail on the subject. Good luck and God bless!