upgrade v. 2.8.5 to latest version of wordpress

Visit http://your-domain.com/wp-admin/update-core.php and look for the heading “An updated version of WordPress is available.”

Below that there should a button for “Update Now”. You can update by hitting that button.

If it’s not there then you will have to manually update your website. For that instructions are here.
https://codex.wordpress.org/Updating_WordPress#Manual_Update