Pretty easy. Takes about 30 minutes.

1) Remove brushes/brush holder.
2) Unbolt engine from frame and unhook harness, battery cables and fuel line.
3) Remove (4) bolts holding stator halves together.
4) Pull engine, rotor and front half of stator housing as a unit from back half of stator housing.
5) Seperate rotor from engine using proper wrench on flats of rotor shaft on bearing end. A sharp strike or two on the wrench with a good sized hammer should break the threads loose. Turns off the crankshaft in CCW direction. If stuborn and won't break free, you'll likely have to hold the engine flywheel while stiking the wrench.