The life is a huge book full of lessons. You only can learn the lessons, but you cannot change the lessons, at least a single letter. Not at least a period or comma. You can read it, and learn from it. It is your past. 

The only thing you can do is live in the present moment, right now, right here. Then you can change the future. The only thing that you can change is the future. However, you must understand that to change the future you cannot go there. but you must work in the moment, right now, in the present life. Then, only you can change the future. 

This is the real truth, but unfortunately, most of us do not understand this reality. Thus, we try to change the past, which we cannot at least think of a way. Or we try to go to the future to change it, which is not the proper way of doing it. Then, what is happening? You are ruining your present moment, you are wasting your current moment, which is the only chance to change your future.

Reflect your life, learn from the past, then change the future.