Once you log into your account, click on the "My BookRags" link in the top right corner, then click on the 'Account Information' link. Next to your current email address, click on the Change your email address link. Enter your new email address. re-type your new email address and click the Save button. If you receive no error message, your email has been updated. An email is then sent to your new email address for validation.
Please note: You'll have to validate this address before you can use it to access your account.