Just drop bottom radiator hose and let it drain into a pan.
Generally its a 60/40 mix of G12 or equivalent (think its something like G13++++ now lol) fill up the coolant bottle slowly, let it run and ensure you have water flowing around - careful as coolant level will drop quickly and will introduce air to the system so ensure you have additional coolant at hand. I believe it takes around 6 liters to fill.
Just don't let the water boil over.... alternatively if you are not mechanically minded then take it to your nearest garage for peace of mind, coolant change shouldn'