How to revert mail to Plusnet.

[#1]

I am currently using Thunderbird to handle my Plusnet mail and have decided I would rather go back to handling it in PN.
Could someone advise the quick and secure way to do this - maybe going into Thunderbird and cancelling everything would be the way?

[#2]

I assume you mean that you want to use webmail instead of downloading it
This is probably how http://askubuntu.com/questions/249776/how-can-i-delete-a-mail-account-in-thunderbird

[#3]

Oldjim has answered the question you asked. However to go beyond that if you set up a new account in Thunderbird and use IMAP instead of POP3 when defining the incoming mail server you can use both webmail and Thunderbird to view and respond to messages, as the fancy takes you, and both methods remain synced.
Thunderbird set up guide here.

[#4]

Thanks to both.  I'll think it over before I decide!