What I found that you are using the older version of Cornerstone i.e. 4.2.3 and X theme version 7.1.1. I would suggest you follow the below steps while updating the X theme and the Cornerstone.
Delete the Cornerstone existing one
Update the X theme to the latest version i.e. 8.3.3
After deletion of the Cornerstone, please use the link in the dashboard to automatically install the Cornerstone.
I tried to download the latest Theme X version and upload it into Theme Manager. Please see screenshot of the message that I get. What am I doing wrong?
The process has been already explained in the previous post, if you are not able to find the Automatic Update please download the latest version from your Themeco Account dashboard and deactivate and delete the existing X theme and upload the latest one. Please remember to follow the steps given in the previous post while updating the theme.