Converting email Files

I am currently using a software called Incredimail which I use for doing my emails.

I have quite a few files in which i have stored my old and new emails into these file(i,e Inbox, outbox etc)

Does anyone know how i can change the emails and files from the Incredimail program into the outlook express files.

I uninstalled the Incredimail program and ran the outlook express but i discovered that all my emails files had gone what i hade created in Incredimail.

I can even run the outlook express program ( as default) but yet again i discovered that all my emails files had gone what i hade created in Incredimail.