This should get some answers...I bet!
I know you canīt change all the wrongs but the main points I came to think of:
1.Better armament production as the war grew bigger all the time, since 1939, and at the latest autumn 1940 as Hitler decided to attack Russia
2.Put OKH and OKW together, so there is no mixing in the HQ. ( Did happen on April 25 1945 by General Warlimontīs book, but that was quite late ).
3. Hitler could never be higher than OKH/OKW.
( Well, wasnīt OKW kinda Hitlerīs puppet?? )And maybe Halder away as he was not too fond of Hitler.
4.Goering out of Luftwaffe by Dunkirk
5. Never start a war with the USA unless you are totally sure you can win it. ( at least beat the USSR first )