Migration from Classic TDS to Extended Withholding Tax 
Purpose
This procedure shows you how to migrate from Classic TDS to its successor, Extended Withholding Tax.
In order for the existing documents involving Classic TDS to be compatible with Extended Withholding Tax, you have to migrate the data. But before you can do so, you have make the appropriate Customizing settings, archive old documents, and so on. Follow the instructions given below.

Ensure that no one can post any documents in the company codes during the withholding tax changeover. We recommend that you block your system for all end users and carry out the conversion runs at the weekend.
You must also carry out the migration in a test system before you start work on your production system.
Prerequisites
You have upgraded the SAP System from Release 4.6B to 4.6C.
Process Flow
Preparations
Migrating the Existing Transaction Data and Activating Extended Withholding Tax
Cleaning Up
You
clean up the system.