Change domain feature helps to rename your hosting account and set a different main domain from your add-on domain list.
If you are a Premium, Business or Cloud hosting user, you can always change the main domain of your hosting account. Simply access your hPanel and find Change Domain option in the Accounts section.
NOTE: In order to change a main domain name, you would need to have more than one domain added to your hosting plan. Feel free to check this article on differences between subdomains, add-on domains and parked domains.