Click the Selection tool and select a
region. To implode music, you’ll usually want to select several
staves by SHIFT-clicking them. See Selecting
music for some region-selecting shortcuts.
Choose Utilities > Implode Music.
The Implode Music dialog box appears, asking whether the resultant reduction
should appear on a new staff (at the bottom of the score) or on the top
selected staff (in which case its current contents will be replaced).
Select either New Staves Added to Bottom of
Score or Top Staff of Selection. If you’ve selected a large amount
of music, this process may take time.