Download latest Android KitKat 4.4.4 stock firmware for F6 TV Box from here or from here. Download previous firmware from here.
Model： F6 TV Box
Image file size: 619 MB
Platform: Rockchip RK3128
Model number: rk312x
Boot version: 2.20
FW version: 4.4.04
Build number: rk312x-eng 4.4.4 KTU84Q eng.yangfeihu.20150911.095925 test-keys
Caution: 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.