Well for discs you need to get the right torx screw bit to remove the disc - Removing the disc itself is pretty easy, but you first need to take the caliper off the disc (obviously
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I can't remember how many bolts there are but I believe that you need a 10mm spanner to loosen the bolts on the caliper; You can then take the caliper off but make sure you don't let it just dangle freely - Try and support it with a cable tie or rest it on a high box or something...
Then you can remove the old brake pads pretty easily - They should pop out with a little bit of persuasion with a screwdriver (lightly) - Then pop your new ones in and prise them into place by placing the screwdriver between the two pads and pushing down (this is what I had to do) - Using a bit of copper grease will help you to get these into place (I forgot to the first time
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Then to replace the disc the two torx screws will need to be removed (if memory serves they are #4 but it may be different for a 172) and it should just be easy to pull off - One of mine welded itself into place so it had to be hammered off - Don't be afraid to use a little force to remove the disc as long as you only hit the disc!
Replace the disc, tighten the screws, put the caliper + new pads over the disc and re-tighten the bolts, and it should be all goooood...
It's important not to press the brake pedal until you have replaced all of the pads/discs you are going to replace; This ensures that they are all aligned properly and all clamp as they should do
You may want to consult a Haynes Manual (if one exists for a 172/182) as some of the information may be different; Different torx screws, different size bolts etc