You need to file what is called "a suit to quiet title."  This is essentially where you ask the court to divest the other person of their ownership interest on the fact that they have abandoned the property and have made no contributions to the upkeep (physically or financially) to the property.  You can try to file this type of suit on your own, but if not done properly, it can cause more issues when you go to try to sell the house.  Invest in a real estate attorney who is familiar with this procedure.  Because of their knowledge base, they will be able to get it done more quickly and efficiently for you.