Click on Tools, and then Account Settings
Doubleclick on your POP/SMTP account that needs to be changed.
Click "More Settings" in the lower right part of the window.
Clear the checkbox that says "Leave a copy of messages on the server"
Do not change any other settings on this window!
Hit OK, and keep doing so until your settings are saved.
Next time you download your mail, it will clear out the backlog on the ideaLEVER Mail server.
It WILL NOT delete any messages from your mail store on your computer.