Hold the cap and turn the key clock wise. You may need to turn the cap a little until it is released. Then to replace you have to sort of screw it in clockwise first til it starts to click, then turn the key anti clockwise whilst holding the cap.
ah right no probs.. bloody stunk lol it sprayed on me but im used to the smell since i work in petrol station thanks for the info chaps..hopefull see some of you soon on a meet up