Difference between G minor and B-flat minor in semitones?

If the song is in too high a key, just enter successively larger numbers and select "transpose down".  If there's just a "transpose" function (no up or down), enter a negative number; that is, a number preceded by a dash, e.g., –5.

It's possible that you'll need to transpose the music so low that the accompaniment no longer sounds good.  Because transposing up or down by 12 semitones doesn't change the key, just add 12 to the negative transpose number.  For example, if transpose is set at –8, reset it to –8 + 12, which equals 4.

Anonymous has made some comments that are just plain wrong.  Semitones are not "between notes" or out-of-tune at all.  On piano, for example, if a white key follows a black key (or vice versa), then those keys and the notes they sound are one semitone apart.  In two instances, from E to F and B to C, they are both white keys with no black key between them†.  Those pairs of notes are also one semitone apart.  A semitone is simply the pitch change from one note to the adjacent note.

( † For this reason E-sharp and F sound the same note, as do E and F-flat, B-sharp and C, and B and C-flat. )

The remark "G# I have seen rarely used" is puzzling.  This note appears in the keys of A and E, which are extremely common in guitar-based music.  For music written in the often-used key of G, saxophones all have a G-sharp in their key signatures, as they are "transposing" instruments.

[ EDIT:  By the way, there is "an H note", at least in some regions of Europe, that is equivalent to a B-natural.  Their B is is our B-flat. ]

3 semitones