Ford Fiesta Draining the cooling system

My Son's 1993 Ford Fiesta overheats - block hot, radiator cool, coolant level down.
For me to check the thermostat and/or water pump I believe I need to drain the cooling system.
(1) Can anyone confirm whether it is merely a matter of loosening the drain-plug on the radiator.
(2) Once I've checked/replaced the thermostat/pump is just a matter of tightening the drain plug and refilling (with the correct mix) via the header tank.
(3) Any tips on how to avoid air pockets ?

All help greatfully reveived.
Bazza.

IF NO BLEED POINTS ON THE SYSTEM(normally at the highest points).fill the system slow,run the engine with the cap off,make sure your heater(NOT FAN) is set to HOT before you start,the system should bleed its self.Squeezing the pipes while filling will help expell air.
You don't have to drain down if you check the thermostat as long as the engine is cold.be prepared for water loss.

I think you should investigate WHYyou have lost water,unless it is obvious, split hose etc.

Blockage somewhere in the coolant system? Malfunctioning water pump?

Chris