There is a hollow tube running through the centre of the stand which hooks through two loops on the frame secured by a split pin. Nobody ever greases this tube, so I think you'll find it hard- remove the split pin, and see if you have any movement- soak it with WD40 for a bit, then try tapping the the tube out with a plastic hammer or such like. Once you have loosened it, you will need to drift it out with a similar sized bar. Good luck!
