Don't sweat this one at all.
It is extraordinarily easy, loosen up the spring tension all the way and they pretty much fall apart. The spring retaining clip will fall off and you slide the spring over the end of the shock. Install new spring, slide clip on and start tightening the tensioner to your desired compressed spring length.
You can loosen and tighten the tension quite a ways by hand too, then use the tool if it gets tough.