When should I increase the resistance?

The right resistance per exercise should always be high enough that you can plan to do the next set of 10 movements, but often only manage to do 6 to 8. Then you have exactly the right resistance! This gives the muscle the highest stimulus for muscle growth, and the last repetitions you do are the most beneficial. If you succeed in doing 10 repeats in every set, you should increase the resistance. But, as has been said, never increase the number of repeats or the number of exercises. You should always limit yourself to 7 exercises per training day. It is important to realize that resistance need not be increased in large steps. Small increases of 1-2 increments on the scale are often sufficient.