To use your own domain, either add it as a Parked or Addon Domain in your cPanel.
Use a Parked Domain if you want to access your main website via another name, or
Use an Addon Domain if you want to have a second website accessible via that name
Please be sure the domain's nameservers are set as followed:
*We do not support changing your account's main domain.*
For more information, please see http://x10hosting.com/wiki/How_to_Use_Your_Own_Domain