This is the minefield. A bad firmware download (virus, incomplete upload, wrong hardware revision) will brick your device. Here are the three safest sources for a better download:
The ONT’s lights flickered—power, then PON, huawei hg8145x6 firmware download better
For most users, there are two primary (and safest) ways to update: Why You Should Update Router Firmware Regularly This is the minefield
Disclaimer: Modifying firmware may void your ISP warranty. Proceed at your own risk. Always keep a backup ONT available in case of a rare bricking incident. For most users
Once you have downloaded the firmware, follow these steps to install it: