Log into your Client Area, then click on Domains:
Click anywhere in the row of the domain you wish to edit (ie on the text that says "Active"):
On the next page, in the left navigation bar, click the link that says "Contact Information":
On the next page, you can select from two options.
If you choose "Use existing account contact" the WHOIS information for your domain will be updated with the contact information specified for your client account with us.
If you select "Specify custom information below", you can manually set different contact information.
Note: If you have several domains, and you'd like to update WHOIS info on all of them, you can also use "Bulk changes"
Please open a support ticket if you need any further assistance.