You may want to destroy entries in the History view of Job Manager to:
Destroying entries also deletes the history log items from the database.
Only certain users have the right to destroy history entries. If a user does not have the right, the Tools > Destroy History Entries menu item is unavailable and has an [x] to the right of it.
You set user rights in Administrator. For more information about setting user rights, see the Prinergy System Administration Guide.