According to the Washington Secretary of State's website, you change the legal name of an Washington LLC by filing a Certificate of Amendment, a one-page, four-line form with a $30 filing fee. See Washington Limited Liability Companies (LLC).If you are unclear on how to fill out this form, if this is in fact the correct form for the purpose you have in mind, or what other forms you have to file, and with whom, once you've successfully changed the name of the LLC, you should consult with a business law attorney in the state of Washington. It's a virtual certainty that you'll have to report the change of name to, at a minimum, the IRS and your state tax authority, as well as to any agency which has issued your LLC any form of business license.