Ganesh, please make use of 'CONDITIONS_IN' and 'CONDITIONS_INX' structures in 'BAPI_CUSTOMERCONTRACT_CHANGE'. Also, make sure to pass the correct parameters along with condition update flag which i'm sure you must be aware of however in case you need any further assistance on this feel free to ask. Thanks.
Just to make sure this is not the same case as someone posted few days ago - you cannot do an update through BAPI that you cannot also do in the transaction manually. First check in the transaction and then post specific error/message you're getting from BAPI. We can't know that if you don't tell us.