Download latest KitKat 4.4.2 stock firmware for EM8S / M8S TV Boxes from here or here. Download from here previous version of firmware for M8S TV Box. To flash firmware on this box from SD card read this article.
Model: EM8S / M8S TV Boxes
Image file size: 475MB
Platform: Amlogic S812 quad core
Update file name: m8s-ota-20150123.zip
Build number: m8s-user 4.4.2 KOT49H 20150123 test-keys
Please do not update firmware unless you know what you are doing, you really want it or it is absolutely necessary. Firmware updates may occasionally have bad results, like bricking your device, temporarily or permanently. The firmware update process is done entirely at your own risk. Before attempting to update the firmware, back up your data.