What is a one-sentence summary of the following article?
The Styrofoam insert might need to be removed as well if the new bumper won't fit. Make any adjustments needed by sanding or grinding carefully. Place the factory bumper on to the new bumper. This can help you accurately drill the holes.

Summary:
Remove the factory-installed bumper, and keep all the hardware for later use. Make sure that the new body kit front bumper lines up correctly. Use the factory hardware to install the new front bumper of your body kit.