I would respctfully disagree with this comment. I don’t think they are equivalent: “Heads-up” has an element of urgency that “update” lacks.
For example, I get back from court and the judge has reserved her decision after listening to oral argument. I send an e-mail to the client, to update them on what happened, tell them how I thought it went, when we can expect a judgment - none of which calls for immediate action on the client’s part.
A week later, the court registrar calls to tell me that the decision comes down in two days. I send an e-mail to the client to give them a heads-up that the decision is coming down, so that they can anticipate any media inquiries or any other prep work they want to do before the decision comes out. “Heads-up” is a warning to them that they have to be ready for something.