After a while the roof lining in the cabrio can start to become grubby, and if the roll bar has any dust on it it is quite common for this to 'wipe off' onto the lining as you lower the roof.
You can try to steam clean the lining in situ, but it's a far better idea to remove and do the job thoroughly.
From the front corner of the roof, where the lining meets the front, gently pull down from the corner.
It is simply held in by a tight press fit of a plastic strip into the roof.
Keep gently pulling the front edge out of the roof.
Open the roof a small amount to 'raise' the first section.
Use a thin watchmakers screwdriver to gently slide the edge of the lining mount off the roof support.
Once it has 'unclipped' off the first leading edge, you can just use your fingers to ease the rest of the mount off the roof support.
'Peel' off the rest of the mount from the supports until it is fully released.
Continue using the same method as before.
Until all the 'main' mounts have been released, and it is only held on by the rear fitting.
The rear fitting is a push fit, like the front section of the roof, gently ease out and pull down the lining starting from one edge.
Now the lining should be free to be removed. (and cleaned!!).
Refit is indeed the reverse of removal, make sure that the front and rear fittings are securely clipped in.