I've done this one mine when I switched out to the black style ones. The top section is really simple, theres a series of screws that secure it to the bonnet, once these are undone it more or less just clips off. The new one then when straight back in using the same screws as before.
The lower one was a pain until I figured out how it was connected. I can't remember if there where screws at each end, but there was a really awkward clip type thing that needed to be undone before it came away. I remember trying to poke at it and wiggling the trim until it eventually came loose. The new one just clipped back on easily.
If I can do it anybody can!
Just remembered there where some plastic rivet type things that had to be removed/loosened when doing the lower part of the grill. Found a couple of photos that might help http://www.northamericanmotoring.com...l-removal.html
The chrome is separate to the grille on the JCW kit lower section just pulls off if I remember right.
When you go to change the lower trim ,cover up the top of the bumper (where trim meets it) with masking tape as when it comes free there is a chance of marking the paint
The cars in front are New MINI Scotland