you have to unclip the main large section first by prizeing the trim from the clips with a srewdriver, get someone to support it when its all off so it doesn't snap off the thin section around the glass. then go around the glass and unclip it. once you have a few off it will get easier, mine just fell off in the end. when you have it off you will probably find the pipe has just popped off pop it back on but don't just leave it like that as i did cos it will come off again very soon!! i stripped one of the cores out of some electrical wire and used it as locking wire, just wrap it around the raised edges you will see where i mean, i also taped it!
you will probably break a few clips everyone does but before you put it back in just spread the remaining clips out. install it the reverse to how it came out.... it is even harder to get it back in! just as a thorght because it is so cold out at the moment, if you can get it in a garage and let it warm up the plastic wont be so cold and brittle, cos you are more likely to break cold plastic!! have fun hope this helps