High End Theme Update

I have read that I need to manually update my theme by removing current theme. I have made changes to the Child theme. So, do I need to delete child theme as well, or just the parent theme?

And if I delete child theme and then install both new themes, do I lose all my data and have to start over again by creating everything again or if backed up, do I just go to back up and reboot?

Thanks,

Marc