Edit: I'm clearly not looking hard enough - I skipped right past it because it was at the very top and not part of the larger list of settings at the bottom.

Thanks timoph!

In the English menu it's Internet connection, then Edit networks

I feel silly, but at least it's something suitably obvious

Weird thing: no sign of any saved Network settings for the router I'm struggling with. I suppose it only saves upon a successful connection.

I'll have another go at this tonight...