Yes you need to remove the bumper.
There are nuts to remove in the fender wells on the left and right sides. The nuts & bolts holding the ends. Then the bracket nuts on the frame rail. All this can be done with the wheels on, just turn them to full lock to gain access to the hardware.
Once the nuts on the brackets are removed you should be able to move the bumper closer in toward the nose. The object of this is to remove the captured bolts that hold the brackets they have a slot that looks like this 'c=' it may be a challenge to remove the bolts.
Once the bolts have been removed, pull the bumper forward slowly so you can control its release.
Now the air dam can be fitted, drilled for attachment hardware and scribed for the bumper ends. Hardware I use are stainless #10 Phillips head screws with neoprene washers and stainless trim washers. I pre-drilled for the hardware based on the Calder Art Car.
My first time I removed the bumper I completely disassembled it and cleaned it thoroughly, they tend to get pretty dirty on the inside.
Once the bumper is 'dry fit' and everything is scribed. It's time for paint. Highly recommend putting a clear bra like Expel. Having repainted my air dam every year for 7 years, the air dam is the most expensive part on the car.
