Couldn't be simpler, really. All the simpler for the fact that they are torsion bars!!
Just crawl under, locate the height adjusters on the back end of the bars, undo the lock nuts, and start unwinding until the desired height is achieved. Do a few roll-and-brakes to bounce it a few times and settle it in, measure that you have the correct ride height on both sides, then remember to do up the lock nuts!!
If you want to get to radical depths, you will need to buy new bars that are set lower, or do what I did and wait 15 years 'till they sagged that much