Update to latest version of WP, PLUGINS, THEMES, PHP version

Hi,
Greetings!

Bought this theme 6 years back, it was working well and good, but website crashed down yesterday, then we restored with old backup. Error was from Ninja form and rev slider.

Is it sufficient to update the WP version and PHP version along with plugin updates instead of updating the theme. Does it work, and can I do page additions, banner additions and everything as usual?

Do we have the latest version of theme under my downloads, can we use that again to update theme in case if required?

Thanks!