Now I am in Shenyang city, China. I already bought round trip train ticket Shenyang-Beijing. It is 177 RMB per 1 ticket. Now I want to change the ticket of Beijing to Shenyang. I want to change date, time and type(to be a train taking 4 hours from Beijing to Shenyang, It is about 218 RMB) Do they charge me? or Do I need to pay any fee for this changing?