This will really depend on how good you are with a set of spanner's, did one recently myself and it was pretty easy, in saying that i am a mechanic?
You will need a 14mm socket and ratchet also a T50 TorX, brake pipe clamp, flathead screwdriver and possibly a G Clamp,
Remove the 2 X 14mm capliper slide bolts & take out one of the brake pads, replace the calpier and push the brake pedal and the free piston will push out to the disk,
put the pipe clamp onto the flexible hose and tighten, then remove the banjo bolt on the caliper to free the brake hose, then remove the caliper,
Put the caliper into a vice and remove the 4 T50 TorX bolts along the back of the caliper,
Reposition the caliper in the vice and rip off the dust cover rubber, youwill see a channel running around the end of the pistons, put the blade of a large screwdriver into the channel and tap the piston out at 180 degree intervals, the piston should come away fairly easy?
With the piston removed pick the dust sheild retainer ring out withe the small screwdriver, you probably wont be able to see it but it is in there,
Just below the retainer ring you will see the piston seal, pick this out also with bthe small screwdriver.
Chances are that the piston itself wont be pitted, just dirty, and that the dust seal retainer ring has rusted and swollen and this is whats making the piston stick,
Scrape away any rusty deposits from the cylidner channels with the swall screwdriver and give it a rub with some emery paper, give the cylinder a good clean out with a clean cloth and some clean brake fluid,
smear the inside of the cylinder with brake fluid, and then the piston seal, locate the piston seal into its channel,
smear a good dollop of cooper grease into the retainer ring channel,
Coat the piston well with brake fluid and align it squarely into the cylinder and push home as far as it will go and then position the dust seal into place replacing the retainer ring,
ease the piston out a little and fit the end of the dust sheild into its channel.
Job Done
Repeat as needed per piston.