I'm not really sure you can. Make them less famous? Certainly. Remove any successes? A Nazi Germany without successes is a Nazi Germany that doesn't have the opportunity to enact the Holocaust. And a Nazi Germany that doesn't enact the Holocaust means Nazism probably has the same status in the West as communism: an uncommon political position, but one that you can always find a few mainstream academics advocating for. Italian Fascism vs. Nazism will probably have similar academic debates as Trotskyism vs. Stalinism.
Committing the greatest war crimes known to man and leaving your country a bombed out wreck that has experienced complete and utter defeat at the hands of its enemies as a result of a war you started is about as legacy destroying as you can possibly get, and that's what the Nazi did OTL.
Committing the greatest war crimes known to man and leaving your country a bombed out wreck that has experienced complete and utter defeat at the hands of its enemies as a result of a war you started is about as legacy destroying as you can possibly get, and that's what the Nazi did OTL.