Comment on How to Update WordPress Themes by SEO Dave.
The child theme issue is almost certainly the size of the child theme, it is huge for a theme and because of the size prone to multiple issues.
Since there’s multiple reasons why a WordPress site can’t install a zip file that’s ~16MB in size (max_file_upload settings, timeout issues, diskspace issues) and the WordPress error messages are about as helpful as an error message that just says “it didn’t work :-)”, when it fails easiest solution is use FTP.
When you unzip the child theme zip file on your PC there should be a folder
within the folder is another folder
ONLY upload the second folder, not the first otherwise things will go wrong.
You should be uploading
so you get
Not tried the above, but my guess would be it will throw out errors before activation and won’t work after activation.
After you have the main theme and child them uploaded you should see these two folders under themes
The number of files you upload is the sort of number you’d expect: actually 1446, but if you were looking through the folders before upload via FTP Windows might have created the thumb index files it creates when viewing images.
So assuming you uploaded the correct folders sounds like you have everything ready for theme activation. You should see both the main and child theme available on your themes page. Now you would activate the child theme.