Sole Proprietorship. Write to us at the address where you filed your return, informing the Internal Revenue Service (IRS) of the name change.This page will walk you through the process step-by-step. If you've changed your legal or business name, you might need to notify the IRS or the Social Security Administration (SSA). To fill out this form, you need to provide the old and new company names, your federal identification number, and contact details. Complete company's legal name as filed with the Secretary of State including "Doing. In order to change your LLC name with the IRS, you'll need to mail them a letter and show proof of the state approving your LLC name change. If the name change is valid, send Letter 147C as acknowledgement. Register their "fictitious name" or "dba" name with the Florida Department of State prior to conducting business in Florida. Partial names, such as Doe, J for John A. Doe, are acceptable.