Looking at your photo...

The "black" visible pulley is the water pump pulley, just to the right, (below) is your crank pulley, to the right of the crank pulley is your belt tensioner. You'll need an E10 (if I recall) inverted socket, which will loosen the belt by shifting counter clockwise. Pulling the fan in front by popping off the front two clips, and unplugging, fan will pull straight up and out, giving you more clearance to work the tensioner.