Nolo Press (
www.nolo.com) has the simplest forms and such. I've formed a number of LLC's using their LLC Maker software package.
I'm my own registered agent. You need a different agent if you are not a person living in the state. For example, if I incorporate a Delaware Corporation with our principal offices in California, I need a registered agent in the state of Delaware. If I form a corp or LLC in the state of California, then I can be my own agent. AFIK, I'm not an attorney, etc.
Don
Edit: I miss-read your question. Yes, just file the change of info form and put yourself in as your agent.