Detach the servo cover plate by removing the 4 Japanese Standard (JS), not Phillips, screws. The servo is probably held in place by a silicone-type adhesive. I once broke an output arm on the aileron servo and replaced it with a spare. The servo was left in place and I poked a hole through the foam to access the servo arm retainer screw. The servo itself was left in the wing.
The servo type is listed in the Habu II Instructions and is probably one of the E-flite micro servos. Check the Horizon Hobby website and search RC Airplanes/Jets for the Habu II. A full listing of spare parts is shown and you can order a replacement servo from Horizon or your LHS. Hope this helps.
Rgds,
Art ARRO