As you go throughout the workout programs within this manual, you're going to find some programs that use low reps. Some programs even have you doing one rep max attempts.
If you're an older trainer, have bad joints, or just don't want to take a chance with low reps, you can definitely increase the reps. You don't have to use low reps.
For example, some of the full body strength specific programs use 5 reps as the basis of the program. You can increase that number of reps from 5 to 8, 10, 12, or even more. Just make sure you decrease the numbers of sets so the overall amount of reps stays constant.
Each rep range has benefits. That's why the programs throughout the manual use so many different rep ranges.
Low reps have different benefits than moderate and high reps.
If you're able to perform low reps safely, please do so.
If you're an older trainer with joint problems, definitely increase the rep ranges so you greatly decrease the risk of injury. If you just want to try higher rep ranges, you can do that too. Just know that different rep ranges provide different benefits.
If possible, you should be performing different rep ranges throughout the different workout programs so you get all the benefits of different rep ranges.
For example, depending on the muscle fiber makeup in your quadriceps your quadriceps might grow better with very high rep ranges compared to low rep ranges or vice versa. They might grow better with moderate rep ranges.
Everyone is different so it's up to you to pay attention to what works best for each muscle group.
One thing that you will notice as you go through workout programs is that the body usually grows in spurts. Once you increase the weight on an exercise to new personal records, you will see your results explode. No matter what the rep range, your body will grow when you reach new levels of weight with each exercise.
Work on increasing the weight no matter what rep range you choose, and your results will be simply amazing.