Transposing from Bb to A clarinet

Change to an A Clarinet then

In order really understand what you mean, we'd need you to attach the score, or a relevant sample, and describe what exactly you want to change. If you really did create a score for Bb clarinet, then changed to Bb clarinet, indeed, nothing should be expected to change, If you changed to A clarinet, it should - assuming you are viewing the transposed score, not the concert pitch score. So make sure the concern pitch button isn't pressed (it normally would not be by default). If it is in concert pitch mode, then unfortunately it means you probably entered the notes incorrectly - you likely entered the transposed-for-Bb notes into concert pitch mode. So the moment you turn concert pitch off, you'll see it transposed as if the notes you entered had been concert pitch. So you'd have to fix that error first, using Tools / Transpose to actually move the notes down a major second.

Do you have "Concert Pitch" enabled? If so, turn it off (click the button).