Short of refilming and redubbing parts of the movie this is the weakest link of the OT.
Stick with what you have and try to work with that to improve it.
You're able to read a lot of posts here, some common things that people do is move Luke on Dagobah to the beginning of the movie and cut a lot of the cutesy dialogue throughout the movie.
In my cut I moved Luke at Dagobah to the beginning of the show.
I also cut Ben entirely. He doesn't really do anything for the movie and just barfs up a lot of things said in the last two movies - aside from talking about Leia.
NOW Luke doesn't know that Leia is his sister.
Later in the movie I had to trim some of the dialogue when Luke and Leia say goodbye. No loss, it's a bad scene that goes on too long and really has a lot to lose.
Now the kicker comes in during the final lightsaber duel. Vader uses the force and when probing Luke's feelings about his friends pieces together that Leia is Luke's sister. NOW we have the other and it also validates Luke losing his s*** during the final saber battle, it is literally a revelation to everyone in the Emperor's throne room, Vader included. It also makes a nice call back for folks who like that sort of thing as it was Vader who told Luke in the last movie that he was his dad, now it's Vader telling Luke he has a sister, too.
Just some ideas for you to work with there, cruise through these boards and you will find more.