I probably shouldn't say anything since I don't have a 6 or that year but I will tell you how it is on my car hopefully that will get you going or someone will say I am wrong!!

On my car ('98 C230) the tensioner pully is spring loaded and has no adjustment. It has an "external torx" head screw on it and you put a wratchet with appropriate E-xx socket on it and pull to remove tension and then release after the new belt is anstalled. At least that is how I remember it and it hasn't been that long ago since I did it.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra