Need to change the user of the train ticket

As for your case, you have to return the ticket of the one who won't go to Shanghai and then have a new one for the another one.

But I notice that they generally don't check the ticket of foreign passegers very carefully, so the one who will come with you may dare to hold the original ticket, no need to change. Anyway, he has to take a risk in case that they check that carefully.