It depends on what option you will choose. If you choose only to change your main domain name, the site will be available under your addon domain name. However it's recommended to not have any addon domain names if you want to change your main domain name because it will cause some issues and some domains will disappear from your cPanel. We recommend to terminate the account from the server and create an account with your new domain name. We will generate a backup of your account before termination so you can restore the files from it in case you need them.