Taking my account from POP to IMAP

Well, firstly, does your mail provider even have IMAP access?

To keep your mail. Create a new mailbox locally Mail-> Mailbox-> New Mailbox. Copy your mail to that mailbox. Then, switch to IMAP, then copy you mail back to the server.

 

yeah...I'm already in line.

It's not just an option you can switch on, man. Be sure your provider actually provides it.

 

This is very important. I made this mistake when I switched to IMAP.

 

Yes, very important. Also be sure to do this for all your sent messages as well. Also note that it may take a fair while to copy all of your messages back to your IMAP server, so open up the mail activity window and let your Mac go, check back on the progress but don't quit mail.
Stopping and quitting mail during this will sometimes result in problems such as heaps of duplicated messages so just let it go. (unless it freezes half way though like mine did ) It might be worth copying your messages over in groups of 200 to be on the safe side.