Visit your campus bookstore or favorite online book retailer.
Search for the book you're looking for. Textbook stores typically arrange books by subject area. If you're looking online, search by the title of the book.
Find multiple editions of the text -- the most recent edition and another edition you wish to compare. If you're purchasing the text for a course, select the second most recent edition to compare.
Open both books to the table of contents. If you're viewing the books online, you should be able to view the table of contents or summary page. Many textbooks will display on the inside cover what changes have been made from the previous edition.
Scan the tables of contents. In history textbooks, look for changes to the most recent years in history; editors often add a few paragraphs about recent events. In criminal justice or politics textbooks, changes may have been made to reflect recent court decisions or legislation. In math textbooks, example problems may be different.
Search for reviews online to see what other people are saying about different textbook issues. Keep in mind that the only way to know for sure is to read or skim the texts yourself.