How to render reports in xlsx extension to a sharepoint library

I set up a report subscription to a sharepoint library and would like to have the reports render in Excel.  But the problem is sharepoint only render it in xls file extension and not xlsx file extension, which is Excel 2007. 

I would like to have it Excel 2007 file format so that this workbook can be called from the dashboard Excel web part.

How can I have the reports render in Excel 2007 file extension?