Let's say that you go back in time to when you were age 10, or 15, or however. Your 10 year old self has all of the memories of your current self. But that's it, you only have your memories of the future, no physical evidence.

IF you wanted to change the future, avert disasters, how could you? You're just a kid, or just a person. How do you convince people to believe you know the future and thus act on your information, rather than just assume you are crazy? An easy example, how could you warn the government of 9/11? You know the day, you know the ones responsible (Bin Laden, Al Qaeda, 19 hijackers), but who do you tell and how do you convince them to take you seriously?

And remember, we are just going based on your memory. So you can't pull out the "On February 1st, the superbowl score is Seahawks 20 v Dolphins 17" or whathaveyou unless you know that fact now.

This assumes of course that the future can be changed, rather than destiny.