How easy to change from POP to IMAP?

[#1]

I have tried on SWMBO's account and managed to get her duplicated with her mail directed, were there any, to another of my inboxes.
AFAICS instructions for this do not exist, at least for Thunderbird.

[#2]

Hi lucerne,
It should be as simple as changing the incoming mail server to imap.plus.net
Let us know if you have any issues after doing that.
Adam

[#3]

Managed to create an IMAP account and all is transferred to it. However in Thunderbird the POP account is still showing, whilst in PN there is (of course?) only the single version, which I presume is now the IMAP one. Have tried to rid Thunderbird of old POP but cannot.
I must be stupider than I have believed, or something is not right.

[#4]

IMAP and POP are two methods of accessing and managing the same information on the Plusnet server, albeit I believe in different storage tables, though an action in one will affect the other. Email clients using POP download messages to the local machine, making them unavailable to any other computer (unless a copy is left on the server); IMAP gives the user's email client more control over that process.
In Thunderbird, if you click Tools->Account Settings,
click on the POP account you want to delete in the left-hand pane, then
click the Account Actions button below that pane, and
select Remove Account
does that do what you want?
Don't want to try it on my account in case it does