Press BACKSPACE
(laptop users Fn-6) or select Edit > Clear All Items. Finale erases all music, leaving empty measures behind.
(If you want to remove the measures too, double-click until the full measure stack is selected and press the delete key. Pressing the DELETE key without a full stack selection erases the music without deleting the measures themselves).
and select a region.
See Selecting
music for some region-selecting shortcuts.