How to export iBooks Author .ipa file to ePub iBooks Author 2.5

Blank ePub template.
Import file. 
Make corrections.
Save. Now there's a *.ipa file.
The export procedure to create an ePub is supposed to be:
Share&gt;Export&gt;ePub.


But ePub is not one of the options.
The options under Share>Export are: iBooks, PDF, Text.
How can I create an ePub file??
I don't know if this will do what you want but have you tried using the app Calibre?  This is a free app for managing e-books. I use it at times to create PDF's from different formats. It manages many different formats. I'd suggest trying it and see if it will do what you want.