How do you change gears on 4 spd Mascio tiller

[Billy Bee]

I bought a used Maschio 7 ft tiller model U 205 in looking at a Maschio website it looks like it has a 4 speed gearbox. I have run this behind my JD 3020 and it spins very fast. I was wondering if I could slow it down maybe I could run it with my 33 hp NH as I am selling the Deere. Anyway, I don't see any levers or obvious way to change the speeds. Does it have to be taken apart, or something simple that I am overlooking?
Thanks, Bill