How do remove all my mail at once?

I want to remove all of my mail in my E-Mail letters all at once? So I can have room for new mail .

Assuming you are using Outlook Express, in each of your folders like Inbox, Outbox etc., left-click the mouse on the item at the top of the list, hold down the shift key and click the one at the bottom. They should all turn blue to indicate they're selected. Then right-click on any of them and select Delete.