Using a 10 mm spanner, unscrew the nipples of the connecting tube of the working cylinders and...
...we pick up the phone.
Using a screwdriver, remove the protective cap.
By forcing compressed air through the brake fluid inlet, we push the pistons out of the cylinders.
We take out the piston.
Using a screwdriver, we remove the sealing ring.
We assemble the cylinder in the reverse order of disassembly. We replace the sealing ring with a new one. During assembly, we lubricate the piston, cylinder mirror and ring with brake fluid.
After installing the caliper on the car, bleed the brake system (see Replacing brake fluid and bleeding the brake system).