Make the nameservers ns1.x10hosting.com and ns2.x10hosting.com Once it updates with those nameservers, go into your control panel and 'park' the domain from the CPanel main page.
It would be the same way you use it with your subdomain, go to your-domain.com:2082, enter your cPanel username and password, and you can manage your webspace from there.
If you want your new domain be your primary domain, instead of parking it, you can change it for your current subdomain at: http://x10hosting.com/account