If you want to put the badges back on, I'd advise you don't. Chances are they are faded, brittle and look old. When you remove them they will prolly show plastic stress lines or snap.
Even if you manage to get them off, you've then got to clean the existing adhesive off the back.
You might as well just buy nice new ones from Fiat.
Also, take accurate measurements of the locations of the existing badges before removal. There's nothing more nasty looking than a rebadged car with the badges in the wrong places (eg. too high up, too low, at an angle due to bad fitting, etc).
Mar '99 1.9TD / 43,000 miles
Current Status: Oddly enough, alright!