On some servers, there may be a file permissions issue when you tried to update/upgrade your WordPress automatically.
In this case, you may need to upgrade/update your WordPress manually via File Manager or FTP.

Before updating, it's always recommended to backup your files and database.

To update/upgrade your WordPress manually, follow these steps:

• Get the latest WordPress at http://wordpress.org/download/
• Unpack the zip file that you downloaded at your local computer
• In the wordpress (at your local computer), rename wp-admin to wp-admin-1 and rename wp-includes to wp-includes-1
• Upload wp-admin-1 and wp-includes-1 from your computer to your server
• At your server, rename wp-admin to wp-admin-old and rename wp-includes to wp-includes-old. Then, rename wp-admin-1 to wp-admin and rename wp-includes-1 to wp-includes
• Upload all new loose/remaining files from the root directory of the new version to your existing wordpress root directory to overwrite them
• Visit your WP Admin once to upgrade the database
• Delete wp-admin-old and wp-includes-old from your server