Apple has just released iOS 11.3 to the public and it is also the first os update for the HomePod, to update the HomePod software simply open the Home app, force press on the HomePod tile and hit detail’s.

You will see HomePod 11.3 (15E217) underneath hit install then agree to the terms and conditions and wait for the update to happen like you would on the iPhone. During the update you will see the Siri light swirl.