The starter motor, itself, is retained by two bolts, only.
To remove the starter, disconnect and isolate battery ground cable, under the seat. It's (should be) the left lug.
On front of motor, toward right, are the two bolts, one above the starter motor, and one below. These are (should be) 8mm wrench size cap head screws. Remove those bolts. Jiggle the starter to the right to disengage the left end.
The left end of the starter snout has an o-ring on a cylindrical boss to block incursion of grime. This cylindrical boss mounts into the left crankcase starter motor mounting hole. The o-ring presents a bit of drag to overcome, in removal.
Once the starter is free, gyrate it around a bit to allow access to the cable, under the black rubber cover. Remove the nut from the cable stud. Alternatively, remove the starter cable from the starter motor first, if you can access it easily with your wrench set.
The starter is free to remove from the machine.
Now, if the starter motor does run (you can just connect 12V to the motor, + to the lug and - to any part of the starter motor metal frame), but the machine won't turn over, then that's another problem.
Starter rebuild is simple, unless something really horrible has gone wrong in there. Replace the brushes and bushings. If something really horrible has gone wrong (field or rotor winding trashed, or commutator gnashed), then take the starter motor/generator shop for rebuild.
Alternatively, just replace the entire unit with a new one, at high cost, or locate one on some auction site, used, probably.
You can check the motor on the machine, without removal. Take a jumper cable from battery + to the starter motor lug. If the starter runs, then you probably don't need to remove it. If this is the case, then you may need to find out if the starter solenoid is failed or if something up line from the solenoid is failed. Instead of connecting a jumper cable, you can jump across the heavy leads of the starter solenoid.
If you need more info on other starter issues (motor turns, but engine doesn't), ask here.