By now, you should feel pretty comfortable with the workouts. Are the weights feeling too light? If you're getting through all five circuits without really needing those two-minute breaks, it's time to increase the intensity.
Increase the difficulty of the bench dips by elevating your feet or putting a weight plate in your lap. Make pull-ups harder by holding a dumbbell between your feet, or put some extra stress on your muscles by slowing down the exercises and pausing at the peak of each rep. Even small changes can pay big dividends by the end of a workout!