Lift as much as you can safely and effectively lift with good form, for the number of reps on the video. I use 30 dumbells for S/H Chest, and I am not huge.
Cathe often uses 25 or 20 lb dumbells for upper body. For lower body she uses as much as a 50 lb barbell, although of course she is strong enough for more.
You, and only you, can determine the right weight. There are no maximums, just what is working for you at any point in time, and that can vary from day to day.