Taking off a car door can be done by removing the door side hinges. However, removing the door may not be a good solution to open the door. Remove the panel of the door and check for a broken rod or loose cable as this may be the cause. These broken parts should be replaced in an automotive store. Before taking off the door, have a mechanic check what might be causing the door to get jammed. Check out http://www.ehow.com/how_7633908_fix-car-door-wont-open.html.