you need to slacken 13mm bolt at top of tensioner, 13mm nut at bottom of tensioner then push back whole tensioner all the way back with big pry bar to overcome tensioner spring pressure. tighten one 13mm up to set it whilst you remove old belt. once new belt fitted loosen 13mm you tightened spring pressure should take up slack in belt. tighten up both 13mm and check tension.
me, March 2009