u guys are very helpful.
the change fee was not 8K. that is what it would cost me to change the ticket (difference in price from when I got RT ticket from BOS-PEK, to todays cost to do muliticity LAX-PEK-BOS).

this is really disappointing, however, that they wouldn't just charge me a change fee and the difference in price of the first leg of the ticket (that is, the difference in cost from BOS-ORD and LAX-ORD). that just makes so much more sense to me. I am not asking to change any other part of the ticket!!