You may remove a mail account from Thunderbird using <b>Account Actions</b> below the list of accounts on the left of the <b>Account Settings</b> tab. Make sure you choose the right account first and don't delete the wrong account by mistake. You'll be given the option to delete only the <i>account info</i> (settings) or also the <i>message data</i>. Choosing <i>message data</i> will only delete mail and folders stored <i>locally on your computer</i> (within your profile folder), not anything stored on the server. Mail <i>on the server</i> will remain there after removing the account from Thunderbird regardless of whether you choose the option to remove <i>message data</i>. Check again in this dialog that the account shown there is the one you want to remove before clicking <b>Remove</b>.