Great Grandfather Name Change - Mantia - Lamento

[Justiceadvocat]

I am in the process of acquiring Italian Citizenship from my Great grandfather Giuseppe Mantia, who when arrived in New York was listed as
La Mantia on boat records, he kept the La Mantia name, his son, my grandfather born La Mantia, but sometime later changed the name to Lamento, which is my father and my last name. What is compelling evidence to show the name change to the Italian government? My grandfather has on his birth certificate La Mantia, however, on his marriage certificate Lamento and death certificate Lamento. Thanks, Charlie