Aside from fall over in shock...cause that would mean I'd met the Big Dude.
What would I do if I would succeed?
End bigotry and hatred.
I would end the placing of ones race, gender, religion, sexual orientation or what not over another's and assuming that one is better. I would make sure that humanity realised again that we are all equals.
Then, you know...after world peace had been achieved, then I'd cure cancer and all that. No point curing cancer when hatred kills more people than that.