DO NOT tension your saddle until you've ridden it many, many, many, many, many, many, many miles!! I have ridden mine 25,000 kms so far and have not had to touch the tensioning yet. Adjusting the tensioning is only necessary after the saddle has been well broken in ... too well broken in that it has started to sag a bit. You tension it to tighten up the sagging. Yours will definitly not be sagging yet.
And the tool is a small flat wrench.
http://www.wallbike.com/brooks/saddlecare.html