It is a paradox that if time travel were possible, you would not dare to go back in time and change anything. To do so, could/would result in an unpredictable and undesirable result. Consider that if someone went back in time and killed Hitler to save the 30 million people killed as the result of WWII, the Soviet Union may have taken over the entire European continent which would have resulted in a war with the U.S. and your ancestors may have been killed before you were born.

I would try to get John Kennedy to use an armored car>

I like the religious historical inventions of some here. But, me, I would go back to March 1967 when Charlie Manson was released from jail, and kill the SOB before he went anywhere else and took so many lives and ruined so many others. No moral qualms about it whatsoever. Like taking out a terrorist before they kill the innocents.

If I could still have my learning ability in place, I would love to observe/learn about how bipeds left Africa.

I‘d kill Hitler before he comes to power. Close second i’d stop the archduke from getting killed, but that wouldn‘t necessarily stop WWI. 3rd stop kennedy assasination,

If I could travel back in time I think I would go back to the early years of Napoleon. Sit him down and tell him to forget about Egypt and England and concentrate on the Louisiana territory. Explain to him that it was loaded with gold, silver and other valuable minerals. He should send France's considerable excess population there rather than into the army.
No other single event is as pivotal and optional as the sale of the Louisiana territory. Not only is the map of North America dependent on it but most of the history of the world is as well.
France could certainly have populated the territory with enough citizens to stop the westward expansion of the US. After the French revolution, France had a very sincere and genuine opposition to slavery. The territory would have served as a sanctuary for escaped slaves and possibly a base from which slave rebellions could have been organized. Even prior to the revolution, the French had a much more tolerant view of native Americans the the US did and it is much more likely that the native American nations would have fared better under France if for no other reason that its hard to do worse than they did in dealing with the US.
Europe would be spared the bloodbath of the Napoleonic wars and developed much more peacefully.
Finally, there would be no Donald Trump. There's no real logic behind that assertion. It just sounds good to say it.

I wouldn't change anything. If I did, I would be different than who I am.

Ahhhhh....there is that point in time in my early years where I wish I could go back and change the outcome of one little accident. I was goofing around with one of my brothers (He is 7 years my senior), so boys do what boys do and next thing I know I am laying on the floor with blood on my face all over. I went down and hit a 90 degrees edge on the floor and off it goes one of my front tooth, well half of it. The nerve hanging and I was in excruciating pain. Years passed by and the half tooth is dead so finally I am being sent to the dentist. This is years ago, technology was eons behind to what it is today. The piece (half anyway) was pulled off (big mistake and you pay dearly for it, you just don't know yet). The Frankenstein dentist (oh I have called him worst than that) build this partial... well, it's been more than 40 years and that little thing over time leads to other problems and it's an endless nightmare that will end when I die..... yeah, that's the thing I would go back to have it changed. Now, do I have any resentment towards my brother? I am glad you ask !!!... the answer is a categorical sound and solid NO. Hey shit happens, that's all there is to it. So no grudges here of any kind. So know you know a little bit more about myself, one of my front teeth is not real (shocking !!!!... I know, right?...well, it's not like we are going to date or anything so, no worries )

I know a standard answer here is to go back and kill baby Hitler. But, I think I would kidnap baby Hitler, try to raise him as a tolerant, good human being. Would be a great nature vs. nurture experiment.

Hitler with the Jews and the Nazis. I'd save all the Jews.

How about going back and sterilising your parents at a young age, ... young age, ...young age, ...young age, ...young age, ...young age...

Nothing..For we mere humans know not how the altering of one event could alter our lives today!

ahhh, I can't make up my mind, The Battle of Badon to understand how battles were fought back then, huge historical battles which really wouldn't have had that many fighters. The Battle of Agincourt to get the truth of it, or the execution of Joan of Arc if I could take my crew with me and mount a rescue, skewering the Bishop of Beauvais in the process.

Emperor Constantine's deathbed conversion, which in turn led to horror and bloodshed.

Go back and wait for Romulus and Remus or whoever to show up, to found Rome.. And shoot them in the balls/sabotage the founding.

Great thinkers, philosophers, show up and heckle them/shitpost over them, make them look like a holes.

I'd go back to the time of Charlemagne and say to him "No, that was just a dream. Trust me on this. You'll win the battle without taking ion that crazy new religion."

Eve and the Apple.

November 2016

Prevent Jesus's crucifixion - no Christianity (while I would be interested talking to Jesus - he seems to be quite reasonable for his time and place)
Stop WW1 - essentially the events that brought WW2 were set in motion back during WW1, thus this is the core event to be prevented - no Nazis, no Hitler, no Soviet Union...
Perhaps there still would be a great war at some point but the world would be different, perhaps better.

None.