If your hot tub is full of water, you need to turn it off and drain it to start cleaning it.
However, you might want to consider flushing the lines of your tub before you do this using a life flush.
This process will get rid of bacteria, mould and other bacteria that you don’t want floating in your hot tub water when you refill it. @thep00lguy often jets the hot tub down as it is draining.
To drain your hot tub, you need to follow the instructions that come with your hot tub, but this often involves using a sump pump or drain plug to remove the water.