Fiat recommend every 75k or 5 years (whichever is sooner), although many people say every 50k or 3 years is a safer recomendation as when to change it.
You shoudl check the belt for cracks/wear, tho if it hasnt been changed within the last 3 years i would do it anyway, saves being broken down somewhere if it snaps. (it wont do any damage if it snaps on the 8v as it is a safe engine)