basically, you need to pay on Western Union website or from a Western Union office (usually, their offices are located in post office or bank office).
You have to tell it's a payment for "Emmanuel Rivoire", then they'll give you a private number that you'll send to me by email (mail form here : http://managames.com/mail_en
I'll use this number to get the money from my local Western Union office.
You can find more details on their website :
If you have more questions, you can send me an email as well.