I never have counted them, but there is about a dozen or so screws that hold the roof on. They are Phillips head screws that are inside the cab. Take those out and the top simply lifts off. While you have the roof off to install the radio, it is a good idea to go ahead and put some insulation inside the top of the roof. The recommended type is the aluminum foil covered bubble wrap stuff. You can buy it at Lowes or Home Depot. I used the recommended 3M spray adhesive to hold the insulation in. The type I mentioned will not hold any moisture and does a good job of keeping the cab cool on the long hot days. If you think your A/C worked well before, wait until you insulate the top of your roof. Just imagine your house without insulation in the attic; same thing.
The radio is easy to install and there is already wires run for the speakers and all. You will need an antenna too. My Kubota dealer goes to NAPA and buys the "rubber ducky" type. He prefers those to the Kubota antennas. Good luck!