I've just been outside to experiment with mine, and you can do it without removing anything! Access is from the back, so you'll need to work from under the car in the dark - there's no way of getting through the grille from the front.
It's much easier to figure out if you've already got the bonnet open! The attached picture is taken from the top with the latch engaged and shows exactly where you need to place a suitable tool - I found the handle of a small 4" adjustable wrench ideal.
You need to lever the release towards the passenger side to unlatch it.
You can reach this from underneath the car without removing the rad cowling - there's a hole in the cowling in just the right place. Either a lucky coincidence, or Fiat have thought this one through. It might help to jack up the front.