Fiat Brava help!

I have had my aerial snapped off my 2000 Brava by idiots passing my house and have bought a second hand one to replace it. I've taken off the panel which also has the light switches and electric sunroof switch on but have been left baffled about where to go from there. There are a number of largish bolts and seems to be a smaller one right at the back which I cannot get to. Can anyone guide me into what I need to do to take off the old aerial stump and screw the new one in?

Thanks