You do not need child theme for update.
Please go through Appearance >> Themes and you can see there update options. Click this link to update. This update doesn’t lost your settings.
Let us know if you have any further query, Our team always ready to help you.
We could not understand why you need child theme? We have no child theme and this update is not related to any child theme. Simply go to Appearance >> Themes and click update link. Your theme automatically update from WordPress repository.
Let us know if you have any questions. Our team always ready to help you.