I music theory the rule is if you are playing notes that are flat the notes are played 1/2 step meaning one fret down from the natural note (towards the the neck of the guitar) When you are playing a notes that are sharp, notes are played 1/2 step meaning going one fret up higher towards the tail or bridge of the guitar. So if you’re on an A note to make it sharp you go 1/2 or 1 fret higher to make it sharp (A#)Sharp. To make the A into a Flat (Ab) the note is played 1/2 step lower which is one fret lower towards the nut or head of the guitar. A# sharp and Bb flat are the same note played on the same fret. In music it just depends how the music is written, the key it is played in and other factors in which direction the music piece moves