With the exception of the Social Security Number (SSN), you can correct any Free Application for Federal Student Aid (FAFSA) field using FAFSA on the Web.
Certain fields, especially those pertaining to your financial information and marital status, should not be changed unless your answers were incorrect on the day your FAFSA was submitted. The fields that should not be changed include "on the day you submitted your FAFSA" in the question.
If you filed a FAFSA using an incorrect SSN, you can change that SSN by either entering the correct one on a paper Student Aid Report (SAR), or asking the financial aid office at one of the colleges listed on your SAR to change it for you. Otherwise, you must file a new FAFSA with the correct SSN. Contact the financial aid office at your college with questions, or to determine if there are deadlines you need to meet.
If you need a paper SAR, you can call the Federal Student Aid Information Center to request a copy. Refer to the Help page for contact information.