If you want to change the domain name assigned as the main one for your hosting account, you can do so in a few clicks!
Step 1 - Check the Domain
Step 2 - Change the Main Domain
Go to Websites → Manage, search for Set Main Domain on the left sidebar and click on it:
Open the drop-down list and choose the domain you want and click on Set as main domain:
You have successfully designated a new domain as the main domain of your hosting account! If you don’t need the old website anymore, you can delete it by following these steps: How to delete a website from a hosting account.
The Set Main Domain feature only renames your hosting account. It has no influence on website files
The option to change the main domain is not available for websites created with Website Builder