The issue you describe Rajesh, is this still on your XI 3.1 environment? Since you said you're planning to upgrade to 4.1.
If yes, then XI 3.1 did not have an option to automatically purge the data.
Please ensure that there was no change made to your Audit database MANUALLY which has caused the old entries to be deleted.
You could directly query in the database for entries prior to 6 months.
The screenshot Ajay has sent is on BI 4.0/4.1 - Its in CMC -> Auditing.
If your database has only 6 months of data, then it is most likely manually purged. The database is the only place your auditing information would remain. If not in the DB, there is no other place it would be found (unless you have audit DB backups taken which contain data before the 6 months).
