I woudln't change anything without a whole lot more thought, because who knows how the world would come out with history changed even in a very small way? One of the ones I would consider the most would be the entry of the US into WWI, perhaps prevented by stopping the sinking of the Lusitania. This would have let the UK, France and Germany bleed each other dry and hopefully let Germany off a bit better from the war and preventing Hitler from gaining power.