There are a couple ways to kill off Hitler
Oster Conspiracy - as the above poster noted if Britain and France defend Czechslovakia and you go to war to them over it, if you fail to capitulate Czechslovakia fast enough there is a chance for the Oster conspiracy to successfully depose Hitler or start a civil war
SS-Wehrmacht rivalry - appoint Himmler to your inner circle. You'll get a bunch of decisions to recruit SS divisions in occupied territories as well as appoint HImmler to field command. Favoring one side too much (and getting their anger too high) will cause events that progressively reflect tensions between the branches. Piss off one side too much and there is a chance for an assassination of Hitler and/or a civil war (operation Valkeryie). If Hitler dies, you get a choice between Himmler, Goering or von Kluge