How do I change what instrument a staff represents?

Just a quick question... I'm having trouble figuring out how to change the instrument of a staff in my score. I don't want to do a mid-staff instrument change; that is well-documented and is not what I'm looking for. I simply want to have a staff be played by a different instrument than the one I had originally planned.

(In particular, when I started writing this arrangement, I wasn't sure what instrument would be playing the saxophone part. I originally set it up as tenor sax, but now that the music is finished I realise that it will sit better in the range of the alto sax, so I want to change it to alto.)

In the instruments menu I can see how to add and remove instruments but I can't figure out how to change the instrument of an existing staff.

Thanks in advance!