Topolino Veloce' should be able to offer some information on this subject, he created his own spoiler which is pretty sweet to have done but sadly many didn't care for the looks so I am not certain how active he is here nowadays. You could try to PM him though. I imagine it is going to require careful removal like any other body panel stuck on with 3M adhesive, fishing line and some heat and a lot of patience and care not to cause damage with the heat...or maybe ask a local shop about it and see if they can offer suggestions or even do it cheaply enough to make that route a better option.
Like Tweak says, it most likely taped on. If you try and take it off. I'd be careful not to dent the roof. Some type of solvent (non harmful to paint) might do the trick to the 3M tape hold ing it down.
why do you want to remove it?