0.) Open destination level in UE4 Editor. Delete Actors that you want to overwrite in World Outliner.
1.) Open Window -> Levels
2.) Levels -> Add Existing (choose source level)
3.) RMB added level -> Select Actors [Selects all added Actors in World Outliner. Choose only Actors you want to move!]
4.) RMB destination level -> Move selected actors to level [moves Actors from Source to Destination]
5.) RMB source level -> Remove Selected [removes Level from destination level]