This post provides Firmware Huawei E355 & E8131s-1 Update 21.157.53.00.00 B757 (Universal), which can be downloaded from the link provided at the end of the post. Once downloaded, extract in a folder using unzip software, and process as mentioned in the respective post. Wrong firmware/software change of a Huawei / ZTE modem/router may dead your device permanently. While running the Huawei firmware update, it will prompt for firmware/flash code as a password. You can generate the firmware code from the universal master code tool.
Disclaimer: Administration of routerunlock shall not be liable if an unknowing change of your modem/router/MiFi firmware. Moreover, if you want any specific firmware related to Huawei dongle / Pocket MiFi, leave a comment; it will be published if it is available. All the firmware publicly posted at routerunlock is free of cost, and there is no need to pay anyone.