There is a locking ring between the holder and the cam. I was able to get that ring out but have no idea how the shellhoder comes out. I have put pliers to it but am afraid I'll bend something. Seems like lee has holders that only fit Lee.
I looked at the directions , looks like it should slide out. Are spent primers backed up into the shell holder ,or rust holding it? If it won't move I would take a dowel and tap on it with a hammer. In the diagram it looks like it slides to the right.
While the press came in a Challenger box, research on the net tells me it is a Classic press. I was given this press by my son's brother-in-law but it is in excellent condition. I still don't have the shell holder out and have emailed Lee. It is rather embarrassing and probably will be more so when I figure it out.