How to remove Duplicate Email from inbox Live Mail.

1.   export the emails you want from the POP account

There is no need to export. Just move them to folders under Storage folders.

4.   Import the POP-EMAILS into your IMAP account....

If the default option to Leave a copy of messages on the serverhasn't been changed, there will be no need to do this. Messages copied from Storage folders to an IMAP account folder will be uploaded to the server at the next sync.

All of the emails are stored on the IMAP server and not on your computer.

This is not normally the case for IMAP accounts in Windows Live Mail. With default settings, all messages are stored on the computer.

All you have to do is change your account settings to IMAP instead of POP3 it's as simple as that. 

Whoa!  This comment is from Microsoft and other mail programs:

You cannot switch between POP and IMAP

• IMAP - stays in-synch with the account your logging in to with all devices
• POP - always gets new messages for the device requesting

Best thing to do is,

1. export the emails you want from the POP account
2. disable your POP account
3. create your new IMAP account
4. Import the POP-EMAILS into your IMAP account.... End comment

And there are other considerations as well.  I'm not sure that this will not bring in your emails again.  IMAP is basically used to be able to check on email from various devices.  All of the emails are stored on the IMAP server and not on your computer.

Another cause is deleting, and then remaking, of an account. 

As for manually deleting emails: when they are in the hundreds?

To remove and then redo the account will CAUSE the duplication of emails.

All you have to do is change your account settings to IMAP instead of POP3 it's as simple as that.