1. Login to your Online Account Manager for this domain name at: http://www.hostingcheck.com/billing/
2. Once logged in, Click On the "Domains" Menu item, then Click On the "My Domains" drop down Menu item.
3. Now, choose the Domain Name in question by finding the domain name and looking to the RIGHT of the domain and clicking the "Manage Domain" Button.
4. Once you are there, Click on the "Nameservers" Tab.
5. Now you can modify your Nameservers right there.
