Rename one to something else. Sonos doesn’t care what the name is, it uses unique ids for each device. The names are just for our eyeballs.

Thanks. But maybe I didn’t make myself clear. I have stupidly added one device to my system twice and given it the same name each time. So want to delete one of those two names. But I don’t seem to be able to. 

Rename one of them, then you can differentiate the two entries and ignore the one that you don't like. If a unit is offline it will  disappear from the list In a few days. You can speed the process by resetting the controller.

Thanks. I’ll give that a try