Yes, don't dismantle anything!
If it's the old type of heater, long and narrow with a polystyrene jacket, you will find the drain outside next to the water inlet. Plastic if I remember correctly, just use a wide screwdriver to remove it. These drain plugs often break or don't reseal well again, spares are plentiful though. If you have the more modern heater which is like a short fat cylinder on its flat side, there will be a yellow lever close by. Lift that lever into the centre position to drain, let it drop horizontal to seal.