To answer your question I need more information. I'll take a stab at it while making a bit of a guess about your current situation. I am assuming that your house will not sell for what you owe on it. As a responsible borrower you are meeting your obligation. Since the loan is in both your names, your "mortgage-ability" is not what you need to purchase the new house. You realize that there are some real good deals out there that you would like to consider. OK, that is my guess of your situation.
Here are your options without bruising your credit: 1) Do nothing and stay in the house. 2) OK, I didn't think you would like that one. You could sell your house and bring the shortage to the closing. That is if you have the cash. If you do have the cash, you might negatively impact your down payment on the new mortgage. 3) If you rent your house as suggested below, you will not eliminate the debt by presenting a signed lease to your mortgage company. That worked pre-2006, but does not eliminate debt today. If you can qualify for the new mortgage without discharging the current mortgage renting might be desirable. Check it out with a mortgage loan provider to determine your exact standing if you lease your home. If you are concerned about becoming a Landlord there are several best practices that you would want to adhere to. I can share them with you later. Being a Landlord can be good experience if you do it right. Any other option, and there are several, will blemish or ruin your credit worthiness. If you have an questions feel free to contact me through Trulia or my web site below.