You can email support@arubanetworks.com and inquire about your account creation (doing so will automatically open a TAC case). Regardless of your access to the support portal, if you have an AP-225, you cannot put InstantOS on it.
There are two modes to meet your management requirements (controller or Instant) as the datasheet shows below. However, you need to choose whether you want an IAP or AP model before buying. If you are in doubt, buy an IAP as it can convert back and forth; however, the "AP" variant model cannot be reconfigured as an Instant.
1) Controller-managed Campus or Remote AP
2) InstantAP running InstantOS