DataTable entry update service query

I have only one entry in my datatable with 4 fields. One of the field is primary key for that datashape. Now my question is i want to update this entry but that primary key value would also be updated. Now the confusion is how can i do that? I have the service UpdateDataTableEntry and AddOrUpdateDataTableEntry but these both services creates a new entry because the value of the primary key changes too. what is the best solution in this regard should i delete the entry first and then add the new one or how you can see this problem?