For the 2000 through 2004 models, there are usually four bolts holding the light unit in place. I say usually because some years I have encountered only have three; missing the one underneath the bumper on the side. Either it fell out over time or there was never one there in the first place.
I find it easier to remove the whole light unit even if I am only changing the bulb as my hand is too fat and my arm won't bend right.
Note: Even though the 2005-07 models share the same basic body style, the headlight units were changed to incorporate the turn signal within it, so I am not sure if these instructions will work.
Here is a video I found describing everything (they did the work on a 2004):
http://www.1aauto.com/1A/HeadLights/Ford/Focus/1ALHP00094
The only thing missing is the 4th bolt underneath the car on the sides, one for each headlight unit. Once you have done everything in the video and the headlight still won't pop out, lay on the ground on the side of the car, forward of the front tire, and look under the fender above the side marker light. You will need a 10mm box wrench as this is a small space...not enough clearance for a ratchet unless you have one of those box wrenches with the ratchet inside.
As a side note, these headlights can be purchased for less than $35 apiece, bulbs included, so if you have cloudy and yellowing units you can replace them easily. I have found that using that cleaning compound to try taking out the yellowing doesn't look like new and in a year they will look worse than before you cleaned them.
Are you asking how to replace the entire headlight assembly -OR- how to replace just the headlight bulb? Just the bulb.
The Ford focus can have LED will headlights. The LED headlights do not come standard on the vehicle and will need to be an aftermarket addition.
You can not replace it unless it's an old ford focus.
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Part number is: HB5
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Yes