I just adjusted the shock by 2 clicks and it made a big difference. I am about 190 lbs / 86 kg and I might want to go one extra click in future.
As mention above all you need to do is to remove plastic covers from left side and seat. No need to do any heavy operations. I used the provided tool and it worked just fine. You can sneak between the frames below the seat , just move the cables to the side and it will work just fine. I am attaching few pictures how I did it (sorry I had to take pictures myself while figthing my 2 year old from eating the fasteners :-D)
As mentioned above to increase the stiffness you want to compress the spring more, meaning you are going to right from looking from the front of the bike, or better you are pushing down on the tool if you go from left side. Just look at it and you will see how it works, easy