Tip: BlackBerry — Removing an E-Mail Account
First, from the home screen, select Personal E-mail Setup-->Email Accounts and then for the account you're ready to part with, simply select "delete." You'll be prompted to confirm your desire.
After completing the task, that account will no longer sync with your BlackBerry and you will no longer see an icon for it on your home screen.
If rather than deleting an account, you'd like to change the settings, go to the same screen (home screen, select Personal Email Setup-->Email Accounts) and click on Edit for the particular account.
Here, you can tell it to sync with your account so that messages you delete from your server are deleted on the handheld. You can change your signature or the way your name is displayed and set an auto BCC if you want to; for example, send yourself a copy of every message.
Be sure to press the Menu button and click "save" after making changes (or say "yes" when you are prompted to while exiting).