Apologies, im not really techno minded... just saw a you tube video where they show a Retina 13inch(2012-2013) being opened up, and the ssd gets upgraded... Its underneath the trackpad, just one screw and the module just clips out and the new one gets clipped in...
Shipping by FedEx is very cheap though. Remember also that customs will hammer you with VAT on 110% of the value and FedEx will charge you a disbursement fee too.