I want to turn my life around. Where do I start?

I am tired of the life i have. I am overweight, have low self esteem, I get pushed around by other people and do nothing about it and I am very lazy when it comes to my education. All my friends tell me that I will never be able to change. I want to prove them wrong. The thing is I am motivated to start this but I want to do it incognito so i can show them in the end that they were all wrong. But where do I start? There is so many things I have to fix in me....