2010 Rav4 D4D V Belt Replacement

[Mc Tavish]

looking for advice or even some idea as to how to do this. I've watched the videos and read the blogs of people that have done it , and to be fair it does look pretty easy ......however ! 

I've striped down car as described removing covers and access panels but i cant see where or how to release pressure from tensioner , the blogs and videos state there is a nut to rotate slowly clockwise on tensioner and belt will slacken and removal replacement is reversal of previous. I do not have a nut to rotate as the tensioner has a cover over centre or am I looking in wrong place?  

Any help would be appreciated or should I just leave well alone , if its not broke don't fix it?

bought new , done 31467 miles after 12 years should use it more!