Hi Ramesh,
Since you are upgrading from SRM 5 to SRM 7 you can continue to use Application controlled workflow itself without any modification.
The only action you need to perform after the upgrade is to change the workflow framework from Process controlled to application controlled workflow. This is because as soon as the SRM version is upgraded, system will set the workflow framework to Process controlled workflow by default, so you just have to change it back to Application controlled using the SPRO configuration.
After the upgrade you have an option to use POWL or UWL as you SRM inbox.
UWL :
In case if you are going to use UWL you need to register all your custom workflow task with Agent assignment , using the steps in the below link. Only after you register the task you will be able to see the work item in your inbox.
Registering a custom Task in UWL - Workflow - SAP NetWeaver BPM Troubleshooting Guide - SCN Wiki
POWL:
If you are going to use POWL then you need to update the below tables with your custom task.
IBO_C_WF_APS
IBO_C_WF_TAS
IBO_C_WF_ACS
No action required if you are using standard SAP tasks.
Regards,
Suresh