Audit records aren't available for export like other record types. You are limited to what is displayed in the Audit Summary. If you are running on premise you could create a custom SSRS report to access the AuditBase table and get the data.
CRM 2011 - reports on data auditing
If running CRM Online you are stuck because you can't get at the tables using FetchXML
You could use the SDK to gather audit data and aggregate it into some sort of organized format.