It's called The Victory Celebration Song. It was one of the things that changed in the special edition releases and to most it was a welcome one. While the original has an ewok chorus chirpping away during the party at the end there, with the lengthened scenes of the celebrations on other planets in the SE's, a change in song and a welcome change in tempo has a much better feel to it. I found this while searching for the name of the song, check this out:
An Analysis Of The Different Musical Endings In Return of the Jedi