To remove rear bumper first unscrew the 10 MM bolt affixed with trans. Now remove the 4 bolts connected inside rear bumper. Now there may be 2 or 4 bolts connecting your bumper from inside of rear wheels tire, remove them too. Pop the plastic rivets off from the place along with underside of rare bumper. At last there would be pop-in-place plastic rivets those are last piece holding your rear bumper. Pull them off and now you can remove the bumper eventually.
This process is similar for major cars perhaps it may slightly differ with few modern car bumpers as available at http://www.iautobodyparts.com/bumpers_components-catalog/. But not to worry, it will not differ utterly, you will be able to address them by own.
luis adkins, February 2015