Place a bench outside the car door that it can rest on while opened and disconnected from the body. Apply masking tape covered with duct tape to the door edge near the hinge side and the nearby fender edge to prevent scratching.
Open the door so it is directly above the bench. Observe how all the fasteners, be they bolts or pins with bushings, are aligned. Generally, the bolts and pins point toward the center of the hinge from the top or bottom, The bolts and bushings are on the body-side bracket for the upper bracket and the door bracket for the lower one.
Remove the detent spring, also called the hold-open spring, from the door by inserting a pry bar up behind it and prying it out. This spring is located behind the upper hinge bracket.
Remove the worn hinge pins or bolts from the hinge brackets. Drive pins out by hitting their pointed ends with a punch and hammer while grabbing the flathead ends with vise-grip pliers. Remove bolts with a wrench.
Pry the door out of the hinge brackets. Support the door by stringing a rope or bungee cord between its upper frame and a roof truss. Otherwise, someone else must hold the door upright while you work.
Inspect the brackets' condition. If they are bent or damaged at all, remove them from the door or body (by removing the bolts) and replace them.
Replace the bushings in the door pin holes if the door has them. Pound the old bushings with the punch and hammer while prying them loose with the pry bar. Press the new bushings into the bracket holes with vise-grip pliers, and tap them the rest of the way in with the punch and hammer.
Align the brackets back into place and screw the new bolts in place, or drive the new pins in with the punch. Insert these fasteners in the same manner as the old ones were attached.
Replace the detent spring. Compress it with a spring compressor, grabbing it with the compressor legs on the spring coils right before the ends. Place the spring in its place between the door and detent mechanism. Loosen the compressor's screw and the spring will slip into place in the door.