Using an external excel spreadsheet as a datasource

I need to use an external excel spreadsheet as a datasource.  This spreadsheet needs to be obtained from a Microsoft website.  A new spreadsheet (currently stored as a zip) will be ADDED each month to the microsoft website, for example the data for December 2016 is currently available and tomorrow January 2017 will be available (this data will be valid from 1/1/2017).

Questions:-

How do I instruct my test case/step to pull in data from an external website?

How do instruct my test case/step to 'on 1st January 2017 use January excel file', 'on 1st February 2017 use February Excel file' and so on.....

I need to do this urgently.

Any ideas would be very welcome.