adding a new instrument

I realize that this may be a very basic question, but I've spent more than a few hours trying to find a solution and have come up short. I've successfully added new instrument sounds, including contrabass clarinet (in Bb). What I want to be able to do is add the contrabass clarinet in Eb to the available instruments to add to a score. How would I do this? My thanks in advance for the help.

-Michael