To change the Bluetooth format on the iFi Audio Zen Air Blue, you can use the device's built-in settings and buttons. Here are the steps:

- Connect the Zen Air Blue to your Bluetooth device.
- Use the front panel buttons to navigate through the settings. Specifically, you need to access the 'Bluetooth Format' or 'Bluetooth Codec' selection.
- The Zen Air Blue supports various Bluetooth codecs such as AAC, aptX, aptX HD, and LDAC. You can cycle through these codecs using the buttons on the device.
- For detailed instructions, refer to the user manual or the manufacturer's official website, as the exact button sequence may vary.

Typically, you would press and hold a button (often the 'i' button or a similar settings button) to enter the settings menu, and then use other buttons to select the desired Bluetooth codec.