Change the key signature in the box at top, then pay close attention when it asks if you want to transpose midi tracks, etc.
This will change all tracks to the new key.
If you don't want that,
You can transpose the one track using 'Edit-transpose MIDI' after highliting the track (I suggest copying to new track and working with that), then change key signature at top (without transposing the tracks), and open notation window... the notation for the one track will be transposed.

*note
audio can not be done this way.


I do not work here, but the benefits are still awesome
Make your sound your own!