Bosch have put a pin in the top of one of the Torx screws that hold the AHS 4-16 hedge trimmer together so you can't get it undone without a special tool. Use a screwdriver that just fits into the top of the Torx screws and hammer it down into the screw head. You should then be able to get the screw undone and when it is out remove the pin. Bosch say you don't need to get the trimmer undone as they don't sell any internal spare parts - you have to buy a new hedge trimmer (but not one made by Bosch!).
Paul
January 2015