1. Change the password for your current (POP3) account in your email client (Outlook, Outlook Express, etc). This prevents a conflict when setting up a new account with the same password.
2. Ignore error messages generated by email client stating that email does not match server settings.
3. Create new IMAP account using instructions listed under the appropriate client on this website.
4. In the email client, drag any emails/folders you want to save from the old POP3 account to the new IMAP account.
5. Depending on the number of emails transferred, this may take an extended period of time.
6. Once all emails are transferred to the new IMAP account, the old POP3 account can be deleted.