Since you don't have a lot of hills, a 14/47 will help to keep the engine RPM's down a little at higher speeds. I can't really speak to what is best for sand riding.
To change the front sprocket, you'll have to remove the left (stator) side cover. You can either drain the oil or lay the bike down on its right side. You should plan on replacing the side cover gasket and you may want to replace the seals (2) on the output shaft and maybe also the gear shifter shaft.
Be careful to note how the wiring is routed and make sure not to pinch any wires when you put the side cover back on.
p.s. Welcome to the forum!