If Hitler had been successfully assassinated in one of the assassination attempts during WWII, who would have most likely taken his place and how would it change the war?

Unfortunately, we simply do not know. The way you've phrased this question makes it sound like a 'what if' question which are forbidden here. You are welcome to ask about Hitler's likely successor, but any questions regarding what could have happened or how it could have changed the war are not welcome here. Please take those to /r/HistoricalWhatIf.