Go to your domain registrar account and put in x10hosting's nameservers. Those namservers are:
ns1.x10hosting.com
ns2.x10hosting.com
Then you need to choose 1 out of the following 3 options:
1. If you don't want to keep your free x10hosting domain, then go ahead and change the main domain to your own domain. Controls to that are in your hosting details in your account panel.
https://x10hosting.com/control/login.php
or
2. If you want to use your own domain as a separate site from your free x10hosting' s main domain's site, then go to your cPanel and click on Addon Domains to place your own domain there.
or
3. If you want to keep your free x10hosting domain as your main domain yet also have your own domain point to the same root site as that main domain, then go to your cPanel and click on Parked Domains to place your own domain there.
Remember, you can only choose one out of those 3 options.