Well, the best way to obtain the software would be to buy a BK-7m, BK-5, or Prelude (version 1) complete with the original disk. I'm not sure that Roland ever offered it for separate download.

However... it was a very "bare bones" software and not at all user friendly. While it's true that you could edit a MIDI in any sequencer program or DAW, you had to prepare it very carefully in the prescribed format, to convert the MIDI to a Roland style.

Really your best option, especially for editing factory styles, is to use the built-in Style Composer. It's not that hard to use and really not that bad. My $.02.