Fatal error(s) when updating

The website (https://savings4.us) appears OK. Howevr,when I try to update plugins, I get this:

Fatal error: Call to undefined function wp_unslash() in /home2/savings4/public_html/wp/wp-admin/includes/file.php on line 914

When I try to update WordPress, I get:

Fatal error: Call to undefined function wp_unslash() in /home2/savings4/public_html/wp/wp-admin/includes/file.php on line 1063

I’m not a php expert, but can basically follow instructions and find my way around in the code —just don’t understand what it says or does always.

Some clues as to what the problem is and how to fix it would be greatly appreciated.

Thanks, Keith