The 2000 Ford Focus is one of the car models where you can't separate the ball joints from the control arms without professional help. If you need to remove a ball joint from the car, you need to remove the entire lower control arm with it. You must replace the ball joint if it has worn down and is loose, which will result in less control of the car while driving.
Loosen the lug nuts on the wheel corresponding to the ball joint you are removing and make sure the car's parking brake is applied. Raise the car's front end with a floor jack, and support the car on axle stands.
Remove the wheel for the ball joint you are removing using the tire iron. Remove the lug nuts in the "five-star" pattern, removing the nut opposite the one you previously removed.
Unscrew and remove the undertray from underneath the engine compartment and out of the bumper well if your car is equipped with one; the screws will likely take a hex wrench.
Remove the clamp bolt nut connecting the ball joint to the steering knuckle assembly using a wrench--take note of which way the bolt is installed for reinstallation. Pry the ball joint away from the knuckle; use a large flat-blade tool if it is stuck.
Disconnect the two mounting clamp nuts located at the rear end of the lower control arm using a wrench, then remove the single nut at the front. Remove the lower control arm and ball joint from the subframe and vehicle.
Make sure you don't damage the ball joint seal with your flat-bladed tool if you need to use one to separate the joint from the knuckle.