Working from memory, when I replaced the horns I managed to remove the grill by: Open the bonnet. The black plastic plastic panel across the front behind the grill and in front of the cross member with the bonnet catch, has four plastic screws. Remove these making a note of which one goes where as they appear to be slightly different. Very gently lift the back of the plastic panel and there are two screws (one either side) carefully using a philips screw driver remove these and the grill can be lifted clear of it's locating pegs at the bottom of the grill. Fiddly but not difficult. Hope this is clear enough.
This was done on a 2010 EX