Legal Question in Civil Litigation in California

You should give notice as soon as practicable, so that the opposing side can prepare for the hearing, or for whatever else notice is given.

Regarding the amended complaint, it all depends on whether the original complaint already was served. If so, then the amended complaint may be served on the same party by regular first-class mail. If you intend to serve an additional party, then you should also have a summons issued on the first amended complaint, and have the new summons and first amended complaint personally served on the new party. Of course, if the new party is out-of-state, you can have another person serve it by certified, return receipt mail.

I'm assuming by answering this that you are the person who was demurred to, and the demurrer was sustained. You need to give notice as soon as possible, and file the notice with a proof of service with the court. You serve the amended complaint on all parties who have appeared, by serving them by mail. If the party demurred, they have appeared, so you will probably have them served by mailing to the attorney. You can't serve by mail yourself, since you are a party. You are going to have to have someone over the age of 18, who is not a party to the action, do the mailing, and sign the proof of service. Then file your amended complaint with the court.

Standby to get demurred to again, and this time it will be doubtful if the court gives you leave to amend.