Before updating the firmware on Particle Photon was a bit tricky. You can use the Firmware updater app on Mac. However I tried a couple of times and never got it to work. Another way was to use the particle-cli but ut was a little messy. You had to download the firmware consisting of two files and the run particle commands with those files in the right order.

However, I just upgraded the the CLI tools (> npm install -g particle-cli) and discovered some new (at least to me) utility functions. Namely particle upgrade.

I connected a Particle Photon with USB, and ran it.

Really simple and worked like a charm!