How do I rename a speaker?

Settings->Room Settings->(Room Name), then select the room name and edit.

Thanks for that but I can't find Room Settings in my Settings options. I'm using the Sonos App on iPhone

If you're running the current Beta a lot of the Settings options are disabled in iOS.

To be honest I'm a novice at this. I haven't changed anything since the original set up approx 18 months ago. Can you advise where and what Beta is? Thanks

OK. On iPhone, open the Sonos app. At the top of the screen you should see the name of the current room e.g. Kitchen or Lounge. Tap on the room name, then tap the gear icon bottom right. Now you should see your current rooms. Tap the room you want to edit, then tap Room Name on the next screen. Select new name from the list.
Beta is software for the controller app that users can sign up to and test for bugs before the new software is released to all users. Best to avoid for now as it removes a lot of functionality from your controller app in iOS. The new software should be out soon.

No gear icon after tapping on room selection. To the left of the room name is a drop down with the settings icon on but after selecting it, no room settings option, as mentioned.

No, that just came to me that I haven't done it. I'll give it a whirl Shirl and follow your advice... Never tangle with a novice! Thanks again

Try updating and see if that works. I've added a screenshot to show the gear icon bottom right.