https://rehubdocs.wpsoul.com/docs/rehub-theme/theme-install-update-translation/updating-theme-and-bundled-plugins/

I am not sure which child theme you use. If you use proper child theme, then you don't need to update it. Child theme can be found here https://rehubdocs.wpsoul.com/docs/rehub-theme/child-themes/how-to-customize-your-theme/

Also i am using child theme so that is need to update ?
Please share with me steps or any tutorial so that i can update theme and other things properly.

Can you please guide me exactly how to update theme and with theme what needs to update also ? 
Becasue i tried myself but still facing issues.

Theme version 19.1 is outdated ? I have purchased theme in October and it is outdated in just 2 months really ?

I am having issue with this theme. I am using Re-cash version of Rehub theme. Theme version 19.1 is giving error on php version 7.4 and not working when i update this to 8.0 or more. I have tried to update theme with latest version to 19.5 but it is also not working with 8.0 or more. I am having performance issue on website so i need to update my php version and theme too.