Shaw instructions show how to create a new account in one of these modes, but not how to change over. I worry that if I delete the existing IMAP account and try to create it again as POP I'll lose access to my emails on the server. My other concern is that the existing emails will stay on the server and not download to my computer.

I realize that it's easier to access emails that stay on the server through multiple devices, but I am getting quota warnings, so I'd rather sacrifice one convenience for better control over my emails. What I'd really like to see is a compromise: keep a week's worth, or a month's, on the server, but download them once they are older than that.