All processes require several steps and in general it is not exactly easy. It is necessary to gather original documents of the ancestors, to perform notary procedures, to file the request in Italy, to disburse high values and to wait some years.
For example, see the documentation required to apply for Italian citizenship by descent.
Original documents from all family members who link you to your Italian relative
You will need the certificates of all people in your ancestry line from Italian to you:
Birth certificate (from the first Italian of your line who emigrated to Brazil, issued by the Comune of birth in Italy or, if it does not exist, the baptism certificate issued by the parish);
Marriage certificate of all in the line of descent;
Death certificates for everyone in the line of descent (if applicable);
Negative naturalization certificate (CNN) from your Italian ancestor.
Documents must be handled in accordance with the Hague Convention to be accepted in Italy and translated into Italian by a sworn translator. Both certificates and translations need to be handled.
Copy of valid ID or passport;
Voter title (original and copy);
Voter’s certificate (with electoral address);
Proof of address;
Certificates (full content and apostiladas);