I'd have tried to be more grateful for what I had as a child, I think. I was such a moody, unhealthy Fi child and I used to have a giant outburst whenever something didn't go my way. A lot of people ended up not liking me, but I never let them know how much I liked them. Same goes for all the teachers I've had, they were all so nice (bar one).
If I had the choice of whether or not *to* go back in time, I think I would (after much wrestling) choose not to... because even difficult experiences have made me into who I am, and all can be redeemed.
However, if I didn't have the choice, and I was thrown kicking and screaming back in time, I would definitely make a lot of different decisions than I did before. Hindsight is 20/20.
But if you changed something in the past, then nothing would be the same today... You're asking an extremely complicated question haha...
I think nothing in the past should be changed, assuming we all learn from the past. Sure, awful things have happened and I wish they never did, but many people need to see those mistakes in order to learn for the future; a shame, but necessary all the same.