How to Upload an ePub File to your Device
To load the EPUB file in iBooks on an iPad/iPhone, etc., add it to your iTunes library choosing File > Add to Library, or drag the EPUB file to the Books library in iTunes on your computer. Then just sync your device with iTunes to add the book to your iBooks library. Alternatively, you can click on the download link you were emailed from your iPad browser (Safari, etc.). That will open up a dialog on your device asking if you want to load the file in iBooks.
Here is a helpful video about how to sideload the EPUB file on a NOOK device.
To load the EPUB file on a Kobo device, use the Kobo Desktop application.