Howdy Abraham,

You'll want to check out the "Transpose instrument key" feature. You can read about transposition using Help/Users Guide and the Index there to look up "transpose".

To transpose the tuba down an octave, you'll want to use
1. Staff/Transpose Instrument key
2. Select the staff, and then either use the drop-list of transpositions, or enter your own values in the appropriate fields.

ttfn,
Sherry