SAPSD Upgrade Project from SAP R/3 4.6C to SAP ECC6.0

Hi Team

As a SAP SD Functional consultant what are the roles and responsibilities need to perform in SAP SD Upgrade Project from R/3 4.6C to SAP ECC6.0 ?

How to identify what are the major differences between R/3 4.6C to SAP ECC6.0 ?

Please provide your valuable suggestions / inputs on the same.

Thanks

Medha