what's the difference between a clarinet in Bb and a clarinet in A?

okay, so i play Bb clarinet and i'm learning mozarts clarinet
concerto, but seeing as its originally written for A clarinet i would
love to be able to play it on that. I just want to know what the
differences are between the two and how hard it would be for me to
start learning the A clarinet. are the fingerings the same? are the
keys different?

thank you :)