New to maintaining my DS III

We've recently inherited a DS III and are competent recreational sailors. We've been enjoying it on the lakes of Vermont and in Barnegat Bay in NJ. But we know almost nothing about the maintenance that this boat needs.
I'm pretty sure that the shrouds are too loose - looking at an old post here it says that they shouldn't be slack until about 10 knots of wind. So my noob question is, how do I adjust the tension?
I can release the tension on the nut in this fitting, but I can't see how to get the fitting to travel up and down the shroud without removing it from the boat. It seems a rather tedious amount of guesswork to unrig, tighten a few turns, re-rig and see if it's too tight or too loose. I'll bet there's a better way.
Love this forum and look forward to learning a lot.
Thanks
Jordan
I'm pretty sure that the shrouds are too loose - looking at an old post here it says that they shouldn't be slack until about 10 knots of wind. So my noob question is, how do I adjust the tension?
I can release the tension on the nut in this fitting, but I can't see how to get the fitting to travel up and down the shroud without removing it from the boat. It seems a rather tedious amount of guesswork to unrig, tighten a few turns, re-rig and see if it's too tight or too loose. I'll bet there's a better way.
Love this forum and look forward to learning a lot.
Thanks
Jordan