Roof Lining Sag

[spasimodo]

So my Clio 172 roof lining is sagging. I've read that it's a fairly 'easy' fix - replacement? but cant find any reference to how it should be done. Any help would be appreciated.
Thanks
Spaz

 

[TC.]

I’m about to fix one in my own by pulling of the sagging bit and recovering with stretch suede with upholstery glue.