It seems you have enable the "change wp-content directory" feature in Better WP Security. This feature often can't work correctly with some other plugins. Did you really enable the change wp-content directory?
Once you have enabled the feature, there is no disable or revert it option. Some suggest you can manually edit the database for bringing it back to normal, but it won't be easy I think. Fortunately, which I've ever tried several times, we can make it works by copying the (missing) files to the new directory.
If the "change wp-content directory" is the cause of your problem, you may try:
1. Locate the missing files
It seems your site has problem with these files:
2. Find the new "wp-content" directory
Do you still remember what is your new wp-content directory? I mean the new name you provide when you activated the feature? If you can't remember it, then you may need to use File Manager or FTP to examine your website's directory structure.
3. Copy the file from your new wp-content directory to (the old) "wp-content" directory
For example if your new wp-content directory is "new-content". What you need to do is:
Copy the file in: .../new-content/includes/upgrade.php
Copy the file in: .../new-content//install.php