The soft headlining is gripped by a metal channel that runs around the whole roof, exception being the front part over the windscreen. It has to be bent open so that the headlining edge can be removed. After putting on the new headlining, with the four rods in place, its edge is being inserted in the channel and the channel edge is being bent back to shape with a mallet, being careful not to damage the headlining fabric and keeping the fabic tensioned at the same time. Easier to describe than do, I have only removed a couple of headlining trims.