Hot tub care is important and you should try and change your tub water once a month. If you are using the tub on a regular basis, then you may want to push that up to twice a month. If you are hardly using your hot tub, or not using it at all, then you may want to go longer. If your hot tub water is dirty, or you see any green in your hot tub, then you will want to change the water immediately. Green means there are algae growing in the water.
Draining a tub is easy to do. If you have a hard hot tub, then there will usually be a drain that usually goes into the main drain of your home. Inflatable hot tubs do not have this. Instead, they have a drain spout on one side of the tub. When you are installing your tub, you should take note of this, and make sure to point it in the direction you want the water to go.
Draining the tub can be as easy as opening the spout and allowing the water to drain out. Try to have the water flow away from any buildings, and towards a drain if possible. If you want, you can attach a hose to the drain to better direct the water. Once you have the water out of the tub, you can clean it as you would normally, and then refill the tub again.