1. Don't try to boil the ocean. You can't change the whole world at once, you can only affect your sphere of influence. You first need to expand your sphere of influence.

2. The easiest way to do that is money. (ex: Bill Gates, Elon Musk) Barring that, you need to write an awesome book, or have something published (Stephen Hawking, Albert Einstein), or get elected (Barack Obama). Chances are, those will lead to increased wealth also.

3. Use that to introduce the change you want in the world.

The thing is, the most difficult part is expanding that sphere. You're one person of 7 billion. That's not even a one in a million chance of impacting the world. The odds are against you. That said, you can make a change in your community, maybe even your city. The key is, you have to start right where you are and impact what you can.

If Albert Einstein had asked 'should I become a patent clerk if I want to make an actual impact on the world?' people would have flat out said NO. The thing is, it did give him steady income and time to think, and thinking is what he did best.

Now of course you can shortcut those steps by being a martyr for whatever cause you want (Nathan Hale, Mahatma Gandhi), but then if you have to ask, you're already doing it wrong.