How do I prepare for the AVAYA exams on my own?

Question

Professional Certification

Share your experience - what are the steps, how long does it take to prepare, what did you use, how did the exam pass and what were the profits after that.
Thanks in advance!
From what I've found:
The Avaya Professional Certification has three levels: Associate, Specialist, and Expert.
Avaya Certified Assotiate (ACA)
To achieve this status, you must pass the Communications Networking exam and one of the elective exams.
Avaya Certified Specialist (ACS)
To achieve this status, you must pass the design exam and one of the elective exams.
Avaya Certified Expert (ASE).
To obtain this status, you must have ASC status + pass one of the elective exams.
It is not clear whether you need to first pass the ACA before the ASC and what kind of exam about design.