Upgrade my 2nd Class France Rail Pass to 1st Class France Rail Pass

I've ordered a 2nd class France Rail Pass for two adults (travelling together) alongwith a 3 yrs old baby (no pass bought for baby). I'm yet to receive the delivery of the pass (as I only booked it last night on www.raileurope.co.in).
However now I want a 1st class France Rail Pass in place of the 2nd class one that I have ordered. Is there a way to upgrade my pass? Can I do it online or do I have to contact the local office? How do I contact the local office since there is no phone number given?

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