My process is as follows:

Bleeding

1. Undo the bottom radiator hose (lowest easily accessible hose)
2. Undo both swirl and expansion caps
3. I wouldn't necessarily undo the rad bleed nut now, but you can
4. I then tend to wash the system through with a hose from down the swirl pot

Refilling

1. Re-fit cap to expansion tank
2. Undo the bleed nut on the radiator (if not done already)
3. Fill with coolant until required amount in the system
4. Make sure not to lose through bleed nut (once it is running out without air then do it up and leave it)
5. Continue to fill until no more will fit

Two methods from here

• My Dad made up an extended funnel arrangement on the end of 12" of pipe that screws into the top of the swirl pot, so it becomes the highest point of the system, use that to fill.

or

• Fill to the maximum in the swirl pot squeezing the top hoses to try to get any more air out of the system ... then remove expansion cap and replace swirl pot screw and run the engine at idle, and allow the system to work the air out of the system through the expansion tank. Run for 5-10 minutes keeping an eye on temperature gauges etc., then refit expansion cap. Turn off car and check the level in the swirl pot.

There should not be any pressure in the system as you have had the expansion cap off, any deficit in the system can then be filled through.
The system takes around 7-8 litres from memory and therefore it is useful to add water in measured amounts so you know exactly how much water and coolant has gone in so you know whether you are close to it's capacity or not.