Hi CS ,
SAP recommand to delete changlog and PSA request which are no longer required.It will good for performance.
If you are sure that you need not required change log data menas that data is already went to respective data target then yes you can delete your changelog requests using process chain or manual.
For how to delete this there is step by setp document present search with "delete request from psa nad changelog sap bi"
Please read and follw the steps.
hope it will help.
Regards,
Ganesh Bothe