URGENT! Can you please help me resolve a Fatal Error?

Hello,

I just updated to the latest version of WordPress and am now receiving this error whenever I click any link from a Post snippet to the full published post.

Fatal error: Class 'WP_Screen' not found in /home4/clinic77/public_html/blackmothersunited.org/wp-content/themes/upfront/elements/upfront-this-post/lib/this_post.php on line 539

I need your immediate assistance!

I look forward to hearing from you soon!

Sincerely,
Kimberly