Do I have to pay cancel costs?

I have booked a K71 ticket for a train trip from Shanghai - Chongqing at 28 November 2011. But now I would like to switch it to a D352/D353 train ticket. This D-ticket is more expensive than the K-ticket. I would like to switch and pay for the difference between prices, but do I also need to pay for cancelling my K71 ticket?