A Moment In Time

You've shot Marty Mcfly by accident and now have the keys to the delorean, What moment In time would you prevent/Create? (It can be personal or a world Issue)

Kill Hitler 

the birth of the first human 

 I'd pull a Biff and go betting millions on all of the winning teams from the last century... 
 
Then I would stop my future children from getting into any major trouble... 

I'd kick Paul Reveres Ass before he could say "The British are coming!"