Swipe Down from the Top of the Kindle Screen and Tap on the Settings option. Click the ‘Devices’ option and then ‘System Updates’. At the top of the screen, it must read “ your device is running Fire OS X.X.X.X.” At the time of this writing, the current version of Fire OS is 5.3.1 or 126.96.36.199.”
Usually, when the Kindle Fire HD/HDX is connected to the wireless network, the device starts updating on its own without any input from the user’s end whenever the new update is available.
Upgrade Kindle Fire Manually