Exchange sleeper card and changing money in China.

Can you tell me about the exchange sleeper card. I book a hard sleeper place (Beijing-Lhasa). After I get in the carriage a conductor will change my ticket for a sleeper exchange card? Usualy how many time after the departure? After I will need back my ticket. Usualy how many time before the arrival?
About changing money. Can I change money in Euros in most of the places/banks? Or is advisable have US Dolars? In airport is easy changing in Euros,right? By the way usualy at what time open the banks in the morning at the airport for changing money?
Many thanks and the best regards.