First of all, is always good habit to do a backup of your page before updating any CMS.

You don't have the backup?

If your page goes wrong after the last WordPress updating, here's how to restore the older version.

All these operations can be done by the Plesk File Manager.

You don't have Plesk? Do it by FTP.

1. Do the page and db's backup
2. Turn all the plugins off and leave WordPress
3. By FTP delete the content of wp-admin and wp-includes (don't delete               folders!)).
4. Upload the package with the older WordPress version except the wp-      content folder, replace the asked files.
5. When the upload finishes, you can go in the login page, click "Update      WordPress Database" when the database updating is necessary.
6. Click "Continue" then turn the plugins on.