Probably a walk through somewhere, however here goes:
Car in gear, wheel off.
Bonnet up, remove cap from brake fluid reservoir and remove some fluid, at least down to min level.
Remove the disc retaing bolt- 10mm i think, careful not to round off, they can be tight.
Knock the 2 pad retaing pins and spring clip out of the caliper from the outer side with a punch or narrow screwdriver. these are just held in with a friction fit collar inboard. Clean up.
Try to slide pads out. You may need to lever the pads away from disc (large scewdriver if replacing both). This will push fluid back into reservoir so check its not overflowing.
With pads removed, the disc may need a tap from the back to release it from hub.
You may need to undo one and loosen the other caliper bolts (19mm) and tilt caliper body up to remove disc. Varies from car to car
IF you do this you MUST release the brake hose from the retaining fixing on strut or you will bend/damage the rigid brake pipe.
Check the seals on the 4 pistons and push the pistons in by hand or with a thick bit of wood (hammer hamdle works nicely) so that they are flush with caliper face (again WATCH fluid level!)
I apply some silicone lube spray to rubber with a cotton bud, to "feed" the rubber and hopefully restore it a bit. The return of the pistons after braking is purely down to the rubber seal pulling it back.
Check and clean up the plated sliding surfaces at top and bottom of the caliper, where the end of the pad slides. Sometimes these are corroded or completely misssing! Touch of copperslip here.
Degrease the new disc friction surface, refit and fit the retaing bolt.
Apply copper slip to back of pads where they contact the piston end, slide in. Tap in retaing pins/refit spring clip. I put a touch of copperslip where the pins fit over spring clip and where the sping clip touches pad edges.
Refit brake line to retaing clip, torque up caliper bolts if removed (some threadlock handy)
Notes - check how good condition bleed nipples are and if you can undo them (10mm) - they are often knackered.