The is an old device (2011–2014 era). If you need better performance or security, consider upgrading to a modern router. For basic use, your current firmware is likely fine, but if you must update, always use ISP-provided files.
To update the software (firmware) on your router, you can use the built-in "Manage Updates" feature within its web-based management page. This allows you to check for the latest versions online and install them with a single click. How to Update Your HUAWEI HG255s Update Software in HUAWEI HG255s
Before updating the software in your HUAWEI HG255s router, make sure: The is an old device (2011–2014 era)
After reboot: