Treble/ bass clefs

How do I move a melody line from the treble clef staff to the bass clef staff or vise versa? Often when I open a MIDI-file in musescore both staffs have a bass clef, In the attached file the notes in the top staff is a bass line and should be in the staff below. I know how to change the clef from bass to treble, but the notes are still stuck in the top staff.