The IAP-207 and AP-207 share identical hardware. The difference is — IAP ships with Instant firmware; AP ships with Campus (controller-based). You can convert a CAP to IAP using a console cable and a TFTP-served Instant image, if you can legally obtain it.
If you cannot access the WebUI or are converting an AP to an IAP, you can use a TFTP server (like SolarWinds) and a serial console cable to push the firmware via the apboot prompt. Key Specifications for Aruba 207 Series Campus Access Points | Product Support
, you typically use the or the device's built-in Virtual Controller interface. While the software itself is technically "free" to download for owners of the hardware, access usually requires a registered account and, in some cases, an active support contract. Where to Find Firmware