Once removed, you need to chisel the lower bearing race up off the lower fork tube. Once this is off, remove the dust cap. Remove the bolts that hold the top and side of the fender on, and lift the fender up over the fork tube. Replacement is the opposite. Make sure to grease the bearings when you put them back in, and check them for pitting.
Replacements are inexpensive.
Tighten the top bearing race until it starts to inhibit the steering motion, Then back it up a tiny bit until it doesn't. Crank the ring nut down hard to lock the race in postion. Reattach your cables and you're done. Rectifiers are specific to the model and year of your scooter. Most rectifiers are color-coded to make it easy to hook up.