Wirelessly posted (8700g: BlackBerry8800/4.2.1 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102)
Go to your carrier BIS account where you set you email account to your BlackBerry. You will find the link here.
http://www.blackberryfaq.com/index.php/Main_Page
"How to sign in to my BIS account" or how to add or delete an email account"