To replace a control arm on a car, remove the old control arm and install a new one in its place, and reassemble the parts. Be sure to obtain an appropriate new control arm that matches your car model.
To remove the old control arm, first park the car on a flat surface, chock the rear wheels, loosen the lug nuts from the wheel where you intend to replace the arm, and lift the car with a floor jack. Remove the lug nuts, detach the wheel from the car, and set it aside. Disconnect the control bar from the sway arm, and detach the ball joint from the wheel hub and the steering knuckle. Loosen off the bolts that secure the control arm onto the frame of the car, and detach the control arm from the car.
To install the new control arm, place the arm in the place previously occupied by the old one, and secure it onto the frame with the mounting bolts. Reconnect the ball joint and the steering knuckle. Attach the sway bar and the control arm, and tighten the ball joint castle nut accordingly. Tighten the bolts that secure the control arm in place according to their torque specifications and torque the sway bar, as well. Finally, reattach the wheel and the lug nuts, remove the floor jack, and fasten the lug nuts.