I know I can make modification in Tiff format but I don’t exactly know how?

Hi, I had read over internet some of best book “how to develop your child personality”. I have downloaded the book but I need to change some of things I don’t agree with and feel they can be harmful for child’s development. This book is in tiff format, I know I can make modification in Tiff format but I don’t exactly know how. Any help appreciated and thanks in advance.