The Select All option selects all chords in the chord table. (see note below).

Once a range of chords is selected, the menu options for operations on all chords of the selected range become enabled.  These are:

Optimize - optimizes the range.  See Chord Optimization.

Raise/Lower Octave.

Clear Score - clears the optimization score.

Clear Signature - resets the signature key of all chords to C Major.

Delete Chords - deletes all chords in the range.

In Table mode, pressing the Ctrl-A keys selects all chords in the chord table.

The menu option Selection > Delete Chords is the only way to delete a range of chords.  To delete all chords use the File > New menu option.

The Raise/Lower Octave operation works only on chords.  Melody notes are ignored.  If raising and lowering  chords and melody notes is desired, use the transpose functions (see Transposing by Half Steps).

The menu option Selection > Clear Signature resets the signature key of all chords to CM (C major)