Can anyone tell me what tool I need to remove the sump bolt on my seicento it appears to be a square hole want to change the oil

Should just be a 10/12mm hex key

12mm hex key, unless it's been rounded off or replaced.

12mm Alen key , It will be quite tight

Could be an after market sump with a square.

If so just try it with either the 3/8" or the 1/2" ratchet

Thanks guys.

i have seen 1/2" drive ones in shop so if not 12mm allen then try as ming says