Change contacts for a domain, follow the steps below: 

1. Login to Control Panel
2. From the menu, navigate to Domains and Websites -> Domain Manager
3. In the domains list, find the domain you want to update and click Edit button
4. In the Edit pop-up section, select Whois card
5. Select type of contact you want to update and click the card for it
6. From the drop-down, select one of the existing contact handlers
7. Repeat 5 and 6 for all contact types you want to update (or use the option to copy data to all contact types automatically)
8. Click Save button
9. Click Close button

NOTE: Some of the contact types might be locked, depending on system configuration.