don't know if it's the 'bulbous' part where the end of the shower hose connects to the middle of the taps needs to be pushed up or down but this i think has been mentioned
If you are having problems raising the collar it is because it is scaled up and will be seized.through lack of use.
What I would do is twist it and try to pull it up at the same time. If you can't get it to move squirt some WD40 into the collar. When it's freed off raise and lower the collar rapidly a number of times and this will free it off.