You'll need more than 2 bottles. If you drain the sump you will get only a fraction of the fluid. Ill just copy from my Stagea post:
Changing the atf is not a simple task but you can do it yourself. Dropping the sump on the auto box will only yield around 1 or 2 litres but at least then you can clean the fiter (its steel) and pan and then put it back together. then take off a hose from the transmssion oil cooler and put it in a 2L plastic bottle and run the engine until you have collected a couple of litres. Stop the engine and pour 2L of new atf down the dipstick (for the auto trans ) and repeat til the oil comes out clean. Could take 10 to 12 Litres