hi,
You have to aware of all related program like BDC's , Screens related errors and all dictionary related problems.
Some function modules may become obsolete, and some screens will change
abnd some new fields will be added in the new versions etc.
Also take care of SPAU and SPDD tcodes.
You should be able to know about Unicode concept in sap.
Upgrading within a new version of SAP R/3 :
The upgrade process for the SAP R/3 application does not modify any of the adapter's ABAP development, but it may modify the SAP R/3 application so that some of the adapter's ABAP development does not work properly.
This section describes how to upgrade the adapter's ABAP development in an upgraded SAP R/3 application. Before you can upgrade the adapter, you must have already upgraded your SAP R/3 application.
To upgrade the adapter's ABAP development:
Install the latest ABAP Extension Module transport files for the correct version of the SAP R/3 application.
You must install the correct version-specific transport files. For details on installing these transport files, see Connector transport file installation.
Compile all programs and resolve syntax errors associated with the ABAP development.
The easiest way to find syntax errors is to generate each function group associated with each object and fix the errors one at time. Repeat this process until all function groups compile successfully. Be sure to generate any other programs such as triggering programs that are not associated with a function group. Be aware that minor updates may need to be made to your ABAP triggering programs after applying the required new transports to upgrade the adapter.
If you are upgrading to SAP R/3 version 4.x, note that the 4.x ABAP handlers use the product namespace /CWLD/. For special considerations for upgrading to the connector supporting SAP R/3 version 4.x, see Connector for SAP R/3.
Test the new environment and make modifications as needed.
Only a full system test enables you to work out any problems with the upgrade. Test your event detection mechanisms by running the appropriate transaction or program and sending business objects to the SAP system. Use the connector's log within the SAP system to help identify other issues.
chk this
http://www.thespot4sap.com/upgrade_guide_v2.pdf#search=%22upGRADE%20STEPS%20-%20SAP%22
also chk these 2 notes in service.sap.com
Technical Upgrade is only a version upgrade without any functionality changes.
The objects that are needed to be upgraded are:
Includes
Function Groups / Function Modules
Programs / Reports
OSS Notes
SAP Repository Objects
SAP Data Dictionary Objects
Domains, Data Elements
Tables, Structures and Views
Module Pools, Sub Routine pools
BDC Programs
Print Programs
SAP Scripts, Screens
User Exits
You can refer to the below links for more information on technical upgrade:
https://www.sdn.sap.com/irj/sdn/wiki?path=/display/profile/2007/05/07/upgradeFROMR3TOmySAPERP-PARTII&
https://wiki.sdn.sap.com/wiki/display/profile/UPGRADEFROMR3TOmySAPERP-PARTIII
http://help.sap.com/saphelp_nw2004s/helpdata/en/60/d6ba7bceda11d1953a0000e82de14a/content.htm
http://help.sap.com/saphelp_nw04/helpdata/en/2e/6d66647d9011d396b60000e82de14a/content.htm
https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/5ac31178-0701-0010-469a-b4d7fa27...
Refer to these related threads
Bluesky
