On this page, you will find the official link to download Lenovo S850 Stock Firmware ROM (flash file) on your Computer. Firmware comes in a zip package, which contains Flash File, Flash Tool, Driver and How-to Manual.
Download Lenovo S850 Stock Firmware (flash file)
File Name: Lenovo_S850_MT6582_S211_140923.zip
File Size: 2 GB
How to Flash: Follow Tutorial