Right.. You know on the drawing, there are little boxes with stuff in?
Well, you click on the one that has the words, lock alpha on it. (Bottom right hand corner)
Under those words, there should be words which say remove and have black dots next to them. You click the black dots.
Sorry if you don't understand that, you could always try this -
viewtopic.php?f=30&t=794080&hilit=How+to+use#p20021078(Credit to Sinamy)