to take the bumper right off, take the 2 torx screws on each side in the wheel arch out T20 i think (maybe a 3rd screw behind the undersheild going upwards best check.);
then theres 4 underneath the bumper.
and then take out the 8mm screws on the top of the grill. you can then pull the bumper from where it meets the wheel arch (lift up and pull) be carefull though has a tendancy to break.
would provide pics but i dont have me corsa anymore.