Hello, friend!
As mentioned in the problem description, the HG8245H5 is a carrier's device.
You can perform the upgrade on the device WebUI. The procedure is as follows:
1. Log in to the ONT using the device administrator account. For details, see:
How to login Huawei ONT
Note: The device is an ISP device. Therefore, you need to contact your local ISP to obtain the administrator account and password.
2. Click Advanced Configuration > Maintenance diagnose tab, and choose Software Upgrade. In the dialog box that is displayed, select the target software version of the device. Click Update to upgrade the software of the device.

3. After the upgrade is successful, a message is displayed indicating that the device needs to be reset. Click Restart. The configuration data takes effect after the device is reset.
For information on how to obtain the device package, click:
How to download the software and firmware of ONT
Thanks!