Ok. Here goes:
Make sure parked on level ground and
coolant is cold.
Do NOT Start the engine
Remove expansion tank filler cap.
Open all bleeds screws -
1) top of thermostat housing near engine lift eye
2) top right of radiator (viewed from in front of car)
3) top of heater hose at back left of engine bay (looks like a tyre dust cap again viewed from front)
Make a header tank by cutting the bottom of an empty 4pint milk container, remove the screwcap and fit upside down into the expansion tank. Seal the joint with duct tape.
Fill the header tank with coolant and watch the bleed screws.
As soon as coolant with no air bubbles comes out of the lowest screw, tighten it and do the same for the other two.
The order should be radiator screw, then thermostat housing screw and finally heater hose screw.
When all screws are tightened, make sure header tank has about 0.5 litre of coolant in it.
Now,
Start the engine
Run at fast idle, just under 2000 rpm and keep an eye on coolant in header tank. You will see air bubbling through and you need to keep topping it up.
Don't fill it too high because as the thermostat opens you will get a big rise in coolant level which will settle down again.
Keep the fast idle running until the radiator fan has cut in and out three times.
Switch off engine.
You now need to remove the header tank without scalding yourself.
The safest way is to get hold of a turkey baster and use that to suck the coolant out of the header tank and into another container. Then you can untape the header tank and remove it without scalding coolant going everywhere.
Check the level on the expansion tank and adjust as required, refit the filler cap and you're all done.