Ok, let's update your live site then, I understand that updating from outdated version to the latest version can be anxious sometimes. But don't worry it should work fine as I don't see any heavy customization you did on the child theme, you might need to adjust a few things after but those are just minor. You can check all the changes, added features, and bug fixes from your current version to the latest version on our Changelog page page.
Before you start updating please CLEAR and DEACTIVATE all your caching plugins (e.g. W3 Total Cache, SG Optimizer, etc) including the server-side caching and CND caching (e.g. CloudFlare, SuperCacher, etc..). This will help us avoid any potential caching related errors.
The first thing to update is the WordPress itself, good thing you already have the latest version (so you can skip this step).
Next is the theme, but since you mentioned above that updating the theme puts your site down, I advise that you deactivate all the plugins first (including all that comes from X) before you attempt updating the theme again.
Since the automatic update might not work because your X and Cornerstone is outdated, please follow the Manual X Update Via FTP guide method in the article below.
Updating Your Themes and Plugins
After you successfully updated the X, we need to update the Cornerstone. with the latest X installed, updating the Cornerstone should be easy. On your admin dashboard navigate to Plugins panel, deactivate and delete the current Cornerstone. Then still on the admin dashboard navigate to X > Validation wait for a few seconds and X will automatically re-install a compatible version of Cornerstone (latest X, latest Cornerstone).
After you successfully update X and Cornerstone, then re-validate your X theme. This is to make sure that you can re-install the latest version of Extensions in the next step.
Then to update the Extensions to the latest versions, that are supported by the latest theme and Wordpress:
- Ensure your theme is validated so Extensions can be installed automatically
- Deactivate and delete the extensions, from the plugins panel.
- On the X > Validation > Extensions, locate and re-install the extensions that you need.
- Visit "Plugins" panel in your Dashboard to activate the newly installed version.
Because all of the plugin settings are stored in the database, and because version 2.x will migrate settings from older versions, its safe to use this method of deleting the previous version.
After that update all your 3rd party plugins.
How to Properly Update WordPress Plugins (Step by Step)
Then activate your plugins one by one and see if something is causing an error.
Again please clear all caches (plugin, server-side, CDN, and browser's cache) after updating so that the code from the latest release is always in use. This will help you to avoid any potential errors.
Follow this guide and your site should be fine, but always keep a backup of the entire site just to play safe.
Let us know how it goes,