First you have to lift the car up and remove the tension, suggest a cut off wheel or try a saw-all. Once you lift the car and remove the torsion bar tension the bolt and nut might wiggle out.
You might also remove the upper bump stop to get a bit more movment in the suspension. Spray it with some wd40 or eqivilent.
Did you have the suspension hanging when you tried to back off the adjuster?
If the adjust bolt was backed out removing the bump stop might help but with tension still on the bar the upper arm will have to be seperated at the bushing bolts or the ball joint.