Hi YelamaReddy susmitha,
If you are interesting in knowing the overview of upgrade process, changes happening in each upgrade phase, building parallel DEV & QAS with proper explanation, then it is better to refer SAP standard guides:
service.sap.com-->Release & Upgrade Info-->Installation & Upgrade Guides-->SAP Business Suite Applications-->SAP ERP 6.0-->SAP enhancement package 6 for SAP ERP 6.0-->UPGRADING AND UPDATING TO SAP ERP 6.0 ENHANCEMENT PACKAGE 6.
You will find all relevant documents here:
1. SAP ERP 6.0 EHP 6 Master Guide: Starting point before starting your upgrade.
2. SAP ERP 6.0 EHP 6 Media List.
3. Software Update Manager(SUM tool) Guides: Process overview in detail.
4. SAP ERP 6.0 EHP 6 Upgrade and Update Guides: Application specific (preparation and follow up activities)
Regards,
Deeraj Shetty