How to complately drain and re-fill coolant 405 TD

I was going to do this to ensure the correct level of anti-freeze and
maybe help prevent problems with a possible head gasket going.

How do i do it - do I need any special techniques e.g. header tank and
how do i get rid of trapped air - is it an issue?

What % of antifreeze should I mix with the water, i'm guessing 30%?

What is the volume of coolant for the 405 1.9 TD (1995).

 

Right; a simple header tank. Take a wide necked plastic bottle eg. a 1 litre
anti freeze bottle and cut the base off. Turn it upside down and stick it
into your cooling system header tank where you take the pressure cap off. Is
it loose? If yes then pack it out with some tape or tissue paper. Make sure
you block off the overflow pipe too and remember to unblock it afterwards.
Unscrew the bleed screws shown in your Haynes manual and fill the system
with you antifreeze mixture until it flows out of the bleed holes.

Good enough for most of Britain.

Haven't the foggiest. Read the manual.