On the 172/182 there are slots in the floor underneath the passenger seat which the craddle slides into, then one screw holds it at the back. The carpet is pre cut so you just need to tear the bit of carpet away to reveal the slots. I assume it's the same for the rest of the range.
I took the changer out of my 172 and put it in my 182, when I came to put it in the Trophy the cutouts in the carpet weren't there as I don't think there is enough room for the changer to fit due to the seats being lower.