The bumper has to come off but it's not tooo severe.
It's held on by two screws inside each wing (behind the headlamp... where the bumper touches the wing) then two or three underneath the radiator support... and the four on top of the radiatore/slam panel. The only nasty ones are the ones under the radiator since they might be seized up... but otherwise it's a simple job for one person.
You need to not try to save time... removed the wheel arch liners to get access to the screws inside the wings, ane don't forget to detach the undertray if you have one.
To remove the headlamps you will also need to remove the bumper mounts. They're just "L" profile pieces of polypropylene (?) like "eyebrows" but underneath the headlamps... held in with a couple of bolts. The lamps foul on them if you don't remove them, so you can't really miss them.
Before you remove the headlamps themselves, point the car at your garage door or house wall and mark the positions of the dipped beam, so you can check the beam angle when you fit the new lamp. Do both sides, since you're going to remove/replace the other lamp too in a minute..
The headlamps are held in by three nuts, attached to a dual-way adjustable stud type screw (#46800136 if yours are rotten) which lets you vary how close the headlamp tabs get to the car body. Don't disturb these if you can help it, or your headlamp aim will change.
The headlamp comes out once you have removed the big round electrical connector on the back.
While you have the bumper off, I would suggest changing ALL the bulbs in both headlamps... otherwise you just know one will blow a week after you do this job and you'll have to wrestle changing the bulb with the headlamp in place... Ahhhh
If it was me/knowing what I do now, I would also change the headlamp adjuster motor in the other headlamp, especially if yours doesn't work, as it's an MOT failure now. If your new headlamp doesn't have one... then order a pair and stick a new one in there too.
I might have a pair of new motors, if you can dig out the number on the yellow label on your motors.
Refit the lamps....check everything works and check that the new headlamp in particular is aimed correctly. You can adjust it up and down by using the outer one of the two white "rod" screws on the back of the lamp. Also check your levellers work...
Then refit everything else, the opposite of dismantling... it'll only take you a couple of hours.
Ralf S.