i finished first free CAT exam at http://www.manhattangmat.com/practicecenter . and cannot find the other five. as i understand they should be six in total? i can review my results, but there should be a link leading to the second CAT and i do not see it in my practice center page...
where is this link?

We offer one free test to anyone. To get additional tests, you have to be a student of ours or you have to buy one of our strategy guides or you have to buy access directly to the tests themselves. If you are in one of these categories, after you take your first test, go back to where you started that first test. You will still see the link that says "New Computer Adaptive Exam." Click on it to start a new test. (It doesn't say test 2 or test 3 or anything like that - it just says "New Exam" every time. Only after you take an exam is it numbered and added to the list of previous exams you've completed.)

If you have just signed up for one free test and nothing else, however, then you will not see an option to take more exams.