If the book has been printed and published, then you can't. The printers can make changes to the type-setting, but only as authorised by the author/publisher, and that will only affect later editions.

But perhaps I have misunderstood your question. Has this book been created using a Word Processor? if so, edit that file. If you mean you have scanned an entire book, and now want to make changes to the text, then you will need some Optical character recognition, (OCR), software. Google will help you there.

Where do you want to do this?

Note, making changes to someone else's publication may contravene copyright laws.