If you are talking about removing the threaded collar below the spring perch [as in my first picture, below] then you should be able to remove it with a motorcycle spring adjustment tool, second picture.
When I adjusted the ride height of my car a few years ago, I found it VERY difficult to move these perches. I suspect they are just stuck. PB Blaster is the ultimate penetrating oil; soak it and let it sit for a few days. The tool fits into the slots on the collar and makes it a lot easier to get it off.
Good luck!
N
