To change the instruments, click the dropdown menu and go to the "Electronic" section. Scroll until you see the bottom of the said section until you see "background arps", "main arps", "chords" and "bass". Click on those, then click on the "Highlight this one" button, which looks like a music note with a box around it. After that, change the instrument from the dropdown menu and repeat the process for each part. (It is optional if you need to have the same instrument for every part.)
