Q: How do I delete a wi-fi network I no longer want?

I was having some connection problems with a guest network (extended off my main network) so I created a new one. Now I want to delete the old one but can't figure out how. I have the new (tall) airport time capsule that I extended out to my old (gen2 flat) airport time capsule. Just want to declutter the list and keep it clean, only mine and the guest. Help please? I know it must be simple, but I couldn't find any help.

Thanks much.