During the final stage of this program, you'll be focusing on higher rep ranges, with all exercises performed as a circuit with time increasing by 50% each round. The reason for this is to push you during the last week and encourage greater muscle definition and separation.
You should select a weight for each exercise that is only about 50-60% of the usual weight you normally use, and stick with that same weight for each round you perform that exercise (It doesn't mean use the same weight for all exercises, just no need to increase the weight on the second and third circuit).
While it may seem light during round one, you'll be performing each exercise a little longer for each additional round, and as you begin to fatigue you'll have to really dig deep and push through it. Keep the tempo controlled but not too fast. You can also slow the negative portion of the rep down as you feel yourself begin to tire.