There is no tensioner per se on the 240. The tensioning is done by moving the alternator. At the top of the alternator there is a tensioning arm with an elongated hole in it. There is a square necked screw which goes through the arm and fastens to the alternator. At the end of the arm there is an adjusting screw. As you are removing the alternator forget about the adjusting screw. Slacken the nut on the square necked screw and push the alternator to the side, releasing the tension. If the alternator won’t move, loosen the flange screw underneath the alternator until it will. With the belt off remove the wires from the back of the alternator, making sure you know which goes where. Remove the two bolts you have loosened and remove the alternator.