For me, I did the second part first. I realized that my life was out of control and that I didn't want it to be out of MY control. I started identifying the ways I felt out of control (anger management, couldn't say "no," so other people were 'running' my life, perpetual negative self-talk that I couldn't stop, racing mind and reliving events long ago from the past that I couldn't let go of). This part I did in my mid-twenties. Then I started thinking of ways that I could change those behaviors I least liked in myself. First and formost was to stop lying for no apparent reason. I still have no idea why I used to do this, but one day I decided I wasn't going to do it anymore. I realized that it was far too difficult to keep the lies up, and much easier if I just didn't lie. So I started fresh, and stopped the lies.
It was much later that I was able to accept peacefully (as opposed to kicking and screaming) that my past wasn't going to change, no matter how much I wanted it to then or how much I want it to in the present. When I could sit at peace with that, I stopped wanting to change my past and started incorporating it into who I am. The pile of negatives became positives. I am strong because of what I lived through. I am resilient because of what I lived through. I am empathetic because of what I lived through. I try to live a life of kindness because of what I lived through. If I had had a different upbringing, I might not have learned all those things about myself. I can sit in peace with my past because my past has helped me be the person I am today (not that I'd want to relive the past mind you, but because of who I am today as a result of it).
Not only am I powerless to change my past now, I was powerless to change it when it was my present. I have never had control over the actions of those in my life who have made my life challenging. But I was able to rise to the challenge and able to use the challenges to be a better person and (hopefully) make the world a better place.