Hello,
Thanks for your question on how to change your demo URL to the actual live domain URL. You will first need to purchase a hosting service. If you have one, then you will also need to have a registered domain name. If you have both of these requirements, then you can use the BoldGrid Backup plugin to backup your site and move it to the new location.
I hope that helps to answer your question! If you require further assistance please let us know!
Regards,
Arnel C.