What's procedure to tighten W124 Belt?

[Fintail Fan]

The serpentine belt on my 1992 W124, (139,000), is squeeling like a stuck pig when the car starts and I'm tired of people staring at me! I did a topic search on this, but the past posts mainly discuss the eventual need, and cost, to replace faulty tensioners, which may be what I need, but none seem to explain the procedure for tightening the tensioner if it's not stripped. Upon examination, the belt is loose. I found a bolt at the end of a rod beside what I think is the power steering resevior, but when I turned it, both clockwise and then counter-clockwise, there was no change on the tension of the belt. I turned it carefully and not far each way because I feared stripping the threads, but I may have done so anyway because on other cars I've owned, there was always some other bolt that had to be loosened first, but I can't tell if this car has the same set up.
Also, I'm thinking I should replace the belt, (bought the car three years ago and have never touched the belt). but it seems that in order to get to any of the lower pulleys I'll need to remove the fan shroud and maybe even the fan in order to get my hands down there and to see what I'm doing. Is there a preferred method/procedure for replacing the belt? And is it easier to access all this stuff from under the car or down from the top? Thanks.

1962 MB 220SEb "Fintail" Sedan
1963 Vespa VNB4T Motor Scooter
1992 MB 300TE 4Matic Wagon
1995 Subaru Wagon AWD