So, are you trying to replace the pully that is on the tensioner? I was not aware that you could just get that pully and that the whole tensioner assy needed to be replaced. The alternator will need to come off, then there are three bolts that hold the tensioner on. There is no "idler" pully on that eng. Belt runs around the tensioner, alternator, a/c compressor and crank.
If you do actually have just a pully to put on the tensioner, the bolt may be a left hand thread. Meaning turn clockwise to loosen and counter clockwise to tighten.