Leaking roof windows, discovery 1

Hi everyone. I recently bought a discovery 1 with what seems a list of challenges. I got in it the other day after it was parked up for a few weeks, the seats and everywhere was wet and going mouldy. I've removed the headlining and found the rear roof windows are very wet around the seals. Is it possible to remove them yourself to clean and re-seal them? Also my roof lining materials have separated, what is best to do with it to repair it or replace it. I don't mind having a go at covering it myself if anyone has had any success in doing so.