There are numerous guide on how to remove the caliper..or it's pretty obvious, so I'll leave that to you. Once you have removed it though, you should end up with something like this:
Start by removing the rubber slide guides....just pull and twist them out with a pair of pliers.
Here's the removed guides:
Nest, we need to remove the piston. If you have an air compressor, brilliant, if not, get your foot pump, fit an inflation attachment pretty much all pumps come with, seal/bulk it up with some ptfe tape:
Insert this into the hole where the hose used to go and hold it in tight, it requires lots of pressure to remove the piston! Make sure you block the space in front of the piston, it will not move and then it will suddenly give. Either you have your fingers there and it will hurt a LOT, or if you don't pack it with wood, spanners etc, the piston will fly out, get scratched and is scrap!:
After a lot of pressure the piston will move out, stretching the dust boot with it:
Pull the dust boot from the lip and withdraw the piston:
Again you can just pull the remaining dust boot out with pliers:
Now you need to remove the actual fluid seal. It sits in the hole where the cylinder was. A small screwdriver will lift it out. DON'T scratch any of the internals though! :
Next clean up the piston.
It may take some scrubbing, and rubbing, but it should come up shiny. If any of it is rusted and you can't remove it, then you need a new one! If the internals of the caliper are rusted, it's pretty much a write off. Mine were OK
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