Hello John,
1. You will have to replace the old theme package with the updated theme package. After that, your theme will be updated automatically.
2. If you have changed something directly in the theme and updated your theme. Then the changes will be lost.
And if you change by child theme, And updated the updated version of the theme. So there will be nothing lost in your theme. So we recommend Whenever you change something in the theme, do it through the child theme itself.
If you need any further assistance, let us know.
Thanks & Regards,
ThemeArile