The Huawei HG255s is an older ADSL2+/VDSL2 router (released around 2013–2015). As of 2021, Huawei had already discontinued firmware support for this model in most regions (except for rare ISP-specific security patches). Therefore, "updating" means either finding a final ISP build or upgrading to custom firmware.
If you cannot obtain a file directly from your ISP with your exact region, do not proceed. update+software+in+huawei+hg255s+2021
This is the most direct way to check for and install updates using your browser. Important Note: The Huawei HG255s is an older
192.168.1.2.upgrade.bin.