You can update the email address on your account by visiting your "Preferences" page and clicking on the "Email Preferences" link. Or, you can visit the page directly here: http://www.neopets.com/email_change.phtml.
You will need your password (and possibly your PIN, if you have this set) in order to change the email address on the account. This is for your protection! If you have lost this information, we will not change the email address for you, as you need this information to confirm the account is actually yours!
If you cannot access your account, please visit the Help Center at http://www.neopets.com/help.phtml?task=ticket and submit either a "Password/Account Access Help" or "Birthday/Account Access Help" ticket and fill out the requested information.
Thank you!