What is the best way I can take my book from iBooks and converted into a EPUB format
I would suggest you to use Calibre:


  calibre is a powerful and easy to use e-book manager. Users say it’s
  outstanding and a must-have. It’ll allow you to do nearly everything
  and it takes things a step beyond normal e-book software. It’s also
  completely free and open source and great for both casual users and
  computer experts.


https://calibre-ebook.com/about

There is a conversion discussion here.

You can also try exporting your .ibooks format to .pdf, and using Calibre to convert that to the format you need.  How well these conversions will work you can only tell by testing it.