I was aiming to go to the new date but a close friend of mine has now decided to get married on Sept 18th meaning I can't go to Grenoble on the 17th

I bought my ticket from here:
http://www.spectacles.carrefour.fr/bill ... -GRCOH.htm
I can see up until the 15th of March reimbursements are possible but does anyone know how with that site? I have the ticket here in the UK. Any knowledge/advice would be greatly appreciated folks.
Cheers!