You'll need to convert each component document to the new version, then add them to a new .indb Book file. Persoanlly, I would export each of the CS3 files to .inx, and open those in your new version (saving with a new name so you don't overwrite the originals) and ad those to the new book.
First, set up your subscription to Creative Cloud, and install InDesign CC 2014.
Then open up each of the CS3 files which make up the book and save them as CC 2014 files. Then create a new book with the Book feature.
The book format cannot be "translated" directly from CS3 to CC format.