Answer:
First you buy the correct replacement bulb. The low beam or High beam - H11 or H9, then with gloves or Very carefully with out touching the bulb with your naturally oily fingers you remove it from the packaging. Next on the car remove the wiring harness from the original bulb, then with a simple half twist you pull it out from the back of the headlamp housing. Connect the new bulb with the wiring and twist it into position. Done. Same if you have the optional HID's, but more expensive and delicate bulbs are involved. Do not leave the Head lamp housing without a bulb attached for fear of moisture and or dirt entering.
To get access to the rear of the headlamp housing is the more difficult part. U jack the car up and twist the wheel to one side to get access to the inner wheel well. Remove the pins holding the inner liner and then you should have access. Messy yes, but doable if one has time and patience to do it safely. Car jacks have been known to slip on occasion.