There are 2 big bolts under the bumper, 1 above the exhaust and the other above the towing eye. They are large torx head bolts (can't remember the exact size).
Remove these bolts and the bumper will slide off backwards, then slide it back into place carefully keeping an eye on the side guides. Obviously refit the bolts.
Cheers,
Iain T
2007 Mazda 6 2.0 estate
Political Correctness - A concept based on the idea that its possible to pick up a turd by the clean end !