Removing the starter on a Ford Focus is complicated by first accessing the starter and then getting it out of the vehicle once it is disconnected. This job is easiest if you have access to a lift, but can also be done on the ground by supporting the front end on jack stands. Either way, expect to spend several hours on this particular repair.
Put your safety glasses on. Set the parking brake and open the bonnet. Use the battery terminal wrench to disconnect the negative battery cable. Chock the right side rear wheel.
Loosen the right front lug nuts with the lug wrench.
Slide the floor jack under the front end and lift the Focus up, positioning the jack stands under the frame. Lower the Focus onto the jack stands. Remove the rest of the lug nuts and pull the wheel off by hand.
Climb under until you can see the starter, which is visible through the rear of the right front wheel well. Use the socket set to disconnect the wiring harness going to the starter. Then unbolt the starter from the engine.
Use both hands to pull the starter out through the wheel well. You may need to turn it this way and that to find the proper angle that will allow you to slide it out.
Move the new starter into place, in reverse of how you removed the old one.
Bolt the new starter to the engine and reconnect the wiring harness using the socket set.
Reinstall the right front wheel and hand tighten the lug nuts.
Jack the Focus off the jack stands and then lower it to the ground. Once down, tighten the lug nuts to 85ft/lbs with the torque wrench. Reconnect the negative battery cable.
Before tackling an involved job such as this, it is best to review the procedure in a service manual, such as the Haynes Manual, so you know what to expect ahead of time. Keep the manual handy during the procedure in case you run into the unexpected. Some models allow better access to the wiring harness and starter mounting bolts if you remove the air cleaner box and access the bolts from the top. Examine your Focus to determine which way will give you an easier time of removing these bolts. Most starters come with a core charge, which is refundable when you return the old starter to the store where you purchased the new one. So, keep the packaging and old starter and get your core charge refunded as soon as possible.