One of the most distinctive features of a joint tenancy deed is its ability to transfer property from one owner to the other almost automatically and without probate court involvement when one owner dies. Although joint tenants can own many kinds of assets this way, real estate is the most commonly held property with this right of survivorship. If your co-owner dies, removing him from the deed can be as simple as visiting your county clerk, but this depends somewhat on individual state law.
Request a copy of your co-owner's death certificate. If the estate is in probate, you can ask the executor or administrator for a copy of the death certificate -- she would typically have secured several copies so she could open the estate with the court. You can also ask the funeral home that handled the burial arrangements. In some states, the death certificate must be certified, so you would have to apply to your state or local health department for an official copy.
Call the government office that deals with land and real estate in your county. In some jurisdictions, this is the registrar of deeds. In others, it may be called the county recorder. Ask what other documents you might need to transfer full ownership of the property to yourself. Your county or state might require a signed or even notarized statement from you indicating that you're taking title to the property pursuant to your deed's survivorship provisions. You might also have to make a statement that the individual named on the death certificate and your co-owner are the same person. Some states require a legal description of the property in addition to the description already included in your deed. Others offer preprinted forms so you can simply fill in the required information.
File the death certificate and any additional required documents with the registrar or clerk, and pay the corresponding fee. This is usually sufficient to clear title to the property and vest it entirely in you. You no longer have a joint tenancy; the death certificate terminates it. You now own the entire property.