After uploading in Compose, you can change the assigned instrument of any stave using the Staves and measures tool. This can be done by following the steps below:

1. Choose the Score menu and select the Staves and measures tool.
   
   
   
   
2. Pencil icons appear on each stave. Click the first pencil in the stave you would like to edit. 
   
   
   
   The "Staff properties" menu is revealed.
   
    
3. Use the dropdown menus to select the desired Instrument Family and Instrument (e.g. "Woodwinds" and "Oboe", respectively).
4. Click Apply Changes when finished.
   
   
   
   
5. Transposition should happen automatically according to the selected instrument, but if necessary, expand the Transposition menu under "Staff properties", click Customize transposition and choose the correct key and/or octave (select Keep notation unchanged if you want to maintain note positions but change the key of the stave).