I laugh when people say "I can change the world." Really? The question I would ask "are you even the best you that you can be?" Improving who you are is a full time and lifelong venture. You will never be the best you if you spend your days dreaming about changing the world. Strive to be a better you and who knows? In the process you may inspire and change one person to do the same. If everyone were to do that then who knows what can happen.
Just remember the problem with changing the world to be "better" is that better is subjective. What is better in your mind is different from what is better in each of your friends minds. One of them might think that changing the world means we all are exactly the same and have exactly the same things. Happiness means different things to different people. If someone believes they can change the world then they have no clue of who they are. Always look inward if you want to make anything better. Oh and for all our sakes, please don't change the world unless it's my version of better!