Hi,
The .mid file was probably sequenced with those notes in separate staves for some reason, typically for "stereo spread" (you can check the Pan settings) or because they were using a device that gave some difference in timbre to the individual staves.
To get the notes into a two-handed score:
1. Use Staff/Merge Staves, and select all the staves. This puts all the notes into a single staff.
2. Use Staff/Split Hands, and select the single staff you created in 1 above.
Voila! Life is good
If you find notes on one "hand" or the other that you want to switch, just select the note with a mouse click, hold "Shift" and press the Up or Down arrow key to shift the note to the staff above or below where it currently resides.
ttfn,
Sherry