how do i lift the truck by adjusting the torsion bars
what are the positive an negatives about this adjustment

 

There is a function called "search".

It is sort of mythical though, so I understand your difficulties.

 

Follow the torsion bar to it's end and you will see the adjustment cam and bolt. Tighten the bolt to lift the truck. Just crank each bar an equal number of turns and get an alignment.
Increasing the torsion bar preload will make the initial portion of the suspension's travel slightly stiffer.