All you have to do is use a flat head screw driver or something along those lines and pop the cover off. Make sure you're not trying to take off the whole thing, just the actualy grille which is just the part that's covered in cloth, not the plastic part under it. Good luck.
I found that a swiss army knife worked well...... or for that matter any kind of long narrow knife. Just be careful to not pluck out your eyes when doing that. Just ease it up all the way around and pop it off. You will hear snapping, but as long as you dont rip it off, the clips should not break.