Enhancing standard datasource: 2LIS_08TRTLP, how to remove standard fields?

Hi,

     While enhancing standard datasource: 2LIS_08TRTLP, I could find that there are fields like ROUTE, TDLNR(from table VTTS) which already present in the datasource.  But I want to add these fields from table VTTK instead of VTTS.

     I've added these two fields but I'm getting message: "Field ROUTE exists more than once".  Also, I couldn't remove the field ROUTE from the existing standard datasource.

     I would like to replace ROUTE, TDLNR, with table VTTK from VTTS.  How could i remove existing fields and replace it with this field? 

     Kindly suggest.

     Also, Do I get any document on all the non-enhanced fields of shipment datasource?  Basically, suppose if I want to know all the details of availability in this datasource, where could I get all such documents?

     Kindly suggest me on the above two queries.

Regards,

Antony Jerald.