Just done mine but and I quote my bumper isnt warped.....the cause is, well Im sure but stand to be corrected, rear cab mountings..... anyhow I removed my bumper and bugger I didnt have time to take pics as time was a factor.
Inside bumper near the middle is two metal half moon support brackets, twist them off with a vice grip.
While the bumper is off you can now adjust the two brackets attached to the chassis but without twisting off them half moon bracket the bumper will not go any lower than it is now.
To remove bumper takes tops 20min, getting it right takes forever.