Many times the teacher changes the tests each year to outmaneuver the students' schemes to base their knowledge on old tests. However, many teachers and professors get tired of continual change. So, what some of them do is rotate their tests every year where, after a year or two, the same test rolls around again. It does not hurt to ask. Let your instructor know that the reason you are asking is to get a feel for exactly what he or she expects from you during the exam.
Different teachers test different ways.
That is why you need to know everything there is to know about taking any particular exam. The instructor may let you look at an old test to see the format and difficulty that will be presented. That does not mean that those exact questions will be on the exam, but you will have an idea of what will be expected of you. You can use those old exams to help you study for the next one. You can use them especially if you are taking the course under the same instructor.