You need to prise up the centre part of the two pins in the top of the grill and then lift the grill forward and up and try and reach behind it to release a couple of fixings (one either side) about 75 mm down from the top. A long screwdriver helps to unclip the two side fixings - it is awkward to do and difficult to explain but once you see the side fixings it is fairly obvious how to proceed.
 
It clips into the back of the bumper (if that makes sense) so strictly speaking you need to remove the bumper to remove the grill. BUT most people have managed to do it with the bumper in situ.

Knowing that the bumper needs to come off helps you to understand how to do it with the bumper on, if you know what I mean.