Very tricky, but it slides off sideways.
I know people will cringe, but if we cant move ours we just bounce the end of the speaker gently on the carpet!! This starts the grille 'slide off' and makes it pretty easy to remove.
Try not to be too rough with the grille. Honestly, if you even look at them in a strange manner they dent!!
Lee
BeoWorld - Everything Bang & Olufsen