No, I would not kill Hitler. It has nothing to do with whether I think I would be morally justified in killing someone who would later order the death of millions. I'm not a violent person. I'd be too nervous to get away with slipping poison in his food or drink, I would hesitate too long with a gun in my had and he'd probably take it away from me. A violent attack, like stabbing, strangling, etc. isn't really in me. Maybe I could kill someone in self-defense, but not as a premeditated act. If I'm just me as I am, but living in Hitler's time, that's what would stop me.
I'm not sure it would help anyway. Killing Hitler wouldn't change the rampant inflation and starvation that was occurring before Hitler took power. People were desperate for a leader who could fix things. Someone very much like him could have taken power instead of him. So even if I could bring myself to kill him, I'm not sure that it would be morally right to do so because the alternate outcome would be at best uncertain. The only sure way to prevent Nazi Germany, or something like it from happening, is to prevent the desperate circumstances that allowed Hitler to rise to power in the first place.
(This response has been edited in such a way that it has been rewritten entirely.)