I don't think that you can "adjust" the tension that the tensioner pulley places on the belt. The spring inside the tensioner assembly will push the pulley (and thus the belt) in as far as it can, until either the force of the spring equals the tension on the belt (which is normally what you want), or the tensioner pully reaches the end of its travel allowed by the bracket. If the belt is too long, the pulley reaches the end of its travel before the belt is sufficiently tight. There are only two moving parts on the tensioner assembly - the pulley itself needs to rotate freely, and the arm the pulley mounts on needs to rotate (probably only 30-40 degrees) against the spring inside the tensioner assembly. You rotate the pulley arm against the internal spring with a big lever (breaker bar, socket handle, etc) on the bolt in the center of the pulley in order to release the tension on the belt to remove/install it. When you release the pressure on the lever, the spring pushes the pulley back against the belt to tension it. Assuming that the pulley bolt is a normal right hand thread, that means that you pull on the lever clockwise to push against the spring and release the tension on the belt.