Enter Domain name, select Domain extention and click modify
Select login as "Administrative Contact", enter administrative user ID, password and click "Login"
After login, click "Option 2" (Appoint A New Billing Contact / Appoint A New Technical Contact)
If you want to assign New Technical contact:
Under "Appoint a New Technical Contact", enter your contact "Code" or Enter New information if you do not have Contact Code
If you want to assign New Billing contact:
Under "Appoint a New Billing Contact", enter your Contact Code or Enter New information if you do not have Contact Code
Reconfirm your change by whois your domain at: