Firmware updates are only available in SteelSeries Engine 3, on a Windows PC.
1) Plug in your Stratus XL A&W controller to your PC via the micro USB port located in the battery compartment.
2) If you have not already, download and install SteelSeries Engine.
3) If this is your first time installing, you will be prompted to update the firmware on your device during installation.
3a) If you have already installed, the image of the device will show a "FIRMWARE UPDATE" bar.
4) Allow the firmware update to run completely and leave the controller plugged in until instructed to complete the installation. Do NOT unplug the controller during the firmware update for any reason, as this can brick your controller.