If you want to live into a better world you must start to behave at such. Our world is not the perfect place to live, but it is the only one we have.
To have a great place to live is need to have a great people, and great people is hard to find. A better word meaning better people. And to have better people meaning to change something that allready exist (people).
The people's changing is not a easy way. Is need a great effort, a big heart and a lot of time. You must be ready to sacrifice yourself for that. And probably discouraging is the fact that there is no chance to succeed in that.
So! How to change the world?
You can't. All you can do is being an example for other, that's it.