Change Connection and maintain column mappings

we have a data compare file from old TDP version (not sure about the version), now we upgraded the TDP to version 5.1, however, we found out the connections in old data compare file is not correct (data source been move to a new server), we used TDP 5.1 to open the old DCP and changed the connection to correct one which worked fine, however, we lost all column mappings. could any one shed us some light on updating the connection without losing the mappings? Thanks