Please check the Certification Data Scheet at http://www.arubanetworks.com/resources/certification/
In short, there are different tracks (ACM = Aruba Certified Mobility; then the fourth letter A=Associate, P=Professional, X=eXpert); ACCA/ACCP (ClearPass); AWMP (Outdoor Mesh), ACDX (Design); ACSP (Solution/Integration).
The Certification Data Sheet shows how the tracks are set up, and an explanation per certificatoin and training.
If you work for a partner, the requirements for Tier 1, 2 and 3 are also mentioned in the sheet.
Success in planning your certfication. If you have issues, please contact your partner or Aruba Sales contacts.
Herman