These study guides have been revised to cover the Postal Service Exams™ #474, 475, 476, and 477 which are the tests now used for Post Office job applications (since April 1, 2019). Any preparation you find elsewhere for test #473 is now useless as that test is no longer given.
Having study guides for these tests is vital, since there are few specific skills to practice or study. Improving your chances of getting the highest score possible will be a matter of understanding the question type and becoming familiar with the different formats. These free study guides will help you in both of those areas.