No it's not hard to change the jet at all,,you just have to take 2 bolts out of the air box and take 2 clamps loose and the air box will come right out and then you can just pull the carb. off, turn it upside down and the jet is right there (don't forget to turn the gas off).
As far as bottom end goes you can make a big differance by just putting a pipe on and they'll send your new jets with it,you'll also need to put a clutch kit in and I also dropped down to a 20 inch tire in the rear and that'll also make a dirrerance...
You can find parts at www.rittercycle.com, www.hpd-inc.com or www.hotseatperformance.com..
Hope this is some help.....