I had to replace one of my foglights. I loosened up around half of the under bumper cover and then took out the front bolts from the inner fenderwell. I purshed them back and was able to install the new and remove the old light. This process worked the easiest for me as I was unable to get completely under the car.
2012 Focus SFE with a sunroof and SYNC: Currently 34.2MPG
Dual Clutch Transmission = Junk.