Is form I-824 mandatory, necesary or is it just to update from an immigrant status to a permanent resident status?

You should review the Instructions on the I-824 form as it states what the document can be used to notify USCIS/DOS with respect to five reasons. The notice provided you is a reminder that if one of the stated events occurs, you need to inform USCIS of the change. http://www.uscis.gov/files/form/i-824instr.pdf

Attorney Abbott gives excellent advice here. In addition, it sounds like you should consult with an immigration attorney who can assist you with the rest of your case. You should speak with an immigration who has had considerable experience with family-based cases specifically. Debbi Klopman, ESq. 398 Bergen Street Brooklyn, NY 11217 www.debbiklopmanlawoffice.com [email protected] 718 622 1208 This advice was intended to be general in nature and not to be taken as a legal opinion or legal advice and was not deemed to create an attorney-client relationship

You do not provide enough information to answer the question. You should review the instructions to form I-824 to see if it is applicable to your case, or retain an experienced immigration attorney to review all the facts and advise you accordingly.