Very easy job. Should take no more than a few minutes to remove the main castle. If I remember correctly, you remove the bolt that holds the left turret top (looking at the castle). Then gently pull the castle straight up from the castle gate. This will expose the optos. When replacing the castle, it might help to use a hair dryer to heat the castle a little bit to make it more pliable so it doesn't break or crack. I'm sure someone will chime in if my memory has failed me. Good luck.