How to edit the underlying query for a predefined datasource report?

How to edit the underlying query for a predefined datasource report?

I love love the fact that you can display the data model for a datasource.

I want to edit the underlying query (SQL or is it ZOHO-QL), so that I can relate additional tables and display additional field values.

Maybe i need to clone the report first?? But don't know how to edit the query.