I have a domain on hostbig[dot]com, hosting service is a simple one, with no addons, only one domain hosted, now the question is how can I change my domain, my current domain is " x ", and want to change it to " y " how am I going to do that. From CPanel? Or from somewhere on the website, I don't really know if is the same at all websites, so I hope that somebody that had, or has a hosting plan from this site can give me some info. Thank you!
Have you talked with your host? If you want your default and main domain that is on record changed and switched, you need to talk to them.
You can simply ask your host to change your main domain, and they will do for you. Because If you don't have root access you can not do it your self.
Your provider will do this. Just send them a ticket and ask them to change your previous domain for the new one.
I don't think many hosting provider allow to you change main domain, because it must be see on their policy. Also, I think better way - you can use Parked Domain feature to overwrite new domain on your hosting account.