This is a bit simple task, as simple as for to upgrade wordpress
1. Download desired version of wordpress from here
2. Unzip it and delete “wp-content” folder and “wp-config.php” file.
3. Take full backup of your “content folder” and “Database” from cpanel or ftp
4. Upload the “downloaded wordpress files”, once it done
5. Go to your WordPress login page (WWW.domain.com/wp-login.php).
6. You can find a different screen from your regular screen. “Click on Update WordPress Database”, with a button named “Update WordPress Database”, click button
7. A new window appears “Update Complete”, press continue and login again, its done
If you want to know more about wordpress of any trouble, shoot an email to me: firstname.lastname@example.org