When you recognize something in your neighborhood that needs improvement, when you see a person that needs a hand, when you right someone's wrong, if you are a sincerely good person, when you raise your children to be kind, honest, hardworking adults...you are changing the world.
It is impossible to change the world without hurting people. There are always a few people that will be ill affected by change. But don't let that stop you. "The needs of the many outweigh the needs of the few," - Spock
Pick up a piece of trash on the side of the road, hold a door open for an elderly person, say thank you at the drive through window, give up your seat on the subway for a person that seems more tired then you, smile and say hi as you pass someone in the street, stop and help someone push their car out of the snow. No one person can change the world overnight, it tales everyone, everyday doing a little bit more and maybe, over time, in generations to come we'll have a better society.