How do I overwrite my game data?

How do I overwrite my game data in Shall We Date?: Ninja Assassin+ by deleting my old Game Center account for it on my old iPhone? Because my current data on my new phone is more up to date than the data on my old phone. How do I sync or overwrite the data so it can be the same data as on my new phone ? I also have the Game Center update on both phones .