Using a 15mm socket on a wrench, 'break' off the wheel bolts (slightly loosen) while the car is still on the ground. Jack the rear of the car up and place an axle stand under the sub frame to take the weight off the jack.

Undo the wheel bolts and remove the wheel from the car.

Using a torx socket remove the securing screw from the drum.

Ensuring the wheels are chocked, remove the handbrake and lever the drum off the car whilst rotating it by hand (these can be hard work to remove as the shoes cut a ridge into the inside of the cover, turning the drum while levering will allow it to work free).

Draining the brake fluid before hand is a matter of preference, we always choose to work messy as fully draining the brake system causes no end of airlocks within the ABS unit.

Locate the shoe holding clips (pictured above).
Place a flat blade screw driver or similar on the back of the unit to hold the back of the clip (this will make more sense when your actually doing the job.

With a pair of long nose pliers, stagger the pin and press the retaining clip into the back plate while slowly rotating. The clip can now be moved away but watch that the spring behind the clip doesn't 'spring' away.

Pull the brake shoes forward slowly to give access to the cylinder.

Unscrew the brake union from the back of the cylinder and pop the brake line back slightly to avoid fouling when removing (ensuring you don't bend the metal line).

The wheel cylinder is secured to the back plate with two 10mm bolts, remove them and pull the whole thing free of the housing.

While you have the drum off clean everything thoroughly, removing all brake dust, also make a point of cleaning the union as these get very grubby with time.

Fit the new cylinder and rebuild the drum assembly in reverse of this guide. Bleeding the brakes is vital. When you do this, pay extra attention to the back of the union for leaks.