There are ways of changing ATF. The easiest way is simplu to undo the sump plug as you would an engine oil change and let it drain out. Then re-fill and change the filter before starting up and re-checking the level. This is ok but none of the ATF in the torque converter is drained, so at best you might be changing maybe half the fluid. Unless you are pretty keen it might be best to pay someone to do this if you want all the ATF replaced. Get them to do the power steering as well.
Coolant is much easier. Depending on the car, you might have a drain plug at the bottom of the radiator on the drivers side (RHD) Remove this but be prepared for it to go everywhere. Otherwise remove the lower hose and it also will send fluid everywhere which if hot could also burn. I bought a huge tray that goes underneath which captures it. If I am replacing the thermostat I do this cold and remove the thermostat once most of the coolant has drained. You could well find a fair bit of coolant behind this, which if hot could burn you, so be careful.
With the thermostat/lower hose correctly installed, and the drain plug back in and correctly tightened, I would also replace the top hose before re-filling. I always use the genuine coolant. It may not be cheap but at least it is expensive and works well. Make sure the nose of the car is not pointing down- up is preferable. I start the engine as i start pouring the coolant in. Once it has filled, keep an eye on the temperature gauge, the coolabt level and also occassionally check how hot the top hose is. There is on rare occassions an issue where the thermostat- even brand new ones- do not work, so you don't want to cook the engine! When the thermostat opens the level in the radiator/tank will drop, so keep filling. Once full, put the cap back on. If at anytime the engine temp goes above it's normal reading you know you have a problem- almost certainly there will be an issue with the the thermostat.
I keep an eye on coolant level for the next few days and top up where necessary. And definitely keep an eye on the temp gauge. I've never had issues doing it this way on any car I've done this on.
