Sorry but they are not always that easy to fit (tho they are easy).
If any of the clips break (which some will) when removing the trim the only real option is to remove the wheel arch liner and cut them off from behind with a pair of wire snips (the clips on the exterior trim are not designed to be re-used).
In itself doing that is a 10 minute job and cheap at around £10 a pop - seems the trim is what those who can't drive tend to scuff on your car, much easier than having to deal with a body shop.
To keep the trim in good condition AG Bumper Care is the best option, easy to apply, just the right sheen, very durable and I've still got my original bottle after 3 years of Mini ownership.