Tools/Account Settings, select the new account, then Account Actions at the bottom of the left pane, Set as Default, then select the old account, Account Actions/Remove Account.

Thank you. I had tried that and tried again. Unfortunately, it's not giving me the option of making my new account the Default account. It would let me remove it, but of course I don't want to do that. It won't let me remove the old (no longer existent) account. I can't figure out why that is, but - Any other ideas?

The account at the top of the left pane in Account Settings is underlined and is the Default account. The Default cannot be removed, which is why another account must be set as Default before the other one can be removed. Also, Local Folders cannot be set as Default or removed. Make sure Local Folders hasn't been renamed to make it appear it's like a mail account. In Account Settings, Local Folders has only Junk and Disk Space settings.

Thank you for more information. The account at the topmost in the left pane is the one NOT marked Default. It's the one below that that is the Default, and it has only Trash and Outbox. One thought occurred to me: is it possible that older message I had saved from that account, now in various saved folders, would prevent that account from being changed (unless they were all deleted)?

If this account only has Trash and Outbox in the Folder Pane, it is the Local Folders account, and cannot be deleted. I think you are confusing the Folder Pane with the display of accounts in Account Settings. Do you have the Manually sort folders add-on? It allows the re-ordering of accounts in the Folder Pane, but doesn't affect the Default account. Maybe you should post pictures of your Folder Pane and Account Settings.

Thank you. I don't have any add-ons. Her is a screen shot o the panel I get when I go to Tools and Account Settings. The Lighedge no longer exists, but it's the default account.

Change the Account Name of Lightedge back to its original name, Local Folders. It can't be deleted. You only have one mail account, @hollyjhart, and it is the Default, since it is at the top of Account Settings and is underlined.

Thank you. That doesn't remove that folder, but it does look clearer. But the top level account, underline, still can be removed, and can't be listed as default. I'm guessing that is not something that can be changed. Thank you for you your advice!

Just to clarify, when you have just one mail account, it's the default account, since there's no other, and it can be removed. It's only when you have more than one account that there's a choice to make one the default, and removing the default requires setting another as default.

Thank you, I think that explains things better.