The camera head can only come out once you have the main assembly out. The lens ring has a bajonet connection, seal and glue. Bajonet is anti clockwise to release. All it needs is about 1 mm.

Its quite hard to get any kind of grip on it. Leave it in place if you can.

Don't touch the 4 screws on the back of the camera head, they hold the sensor to the lens assembly.

Here are some pics of the denstist tools I used to break the little latches and get under the button.