Download latest Android KitKat 4.4.2 stock firmware for MK808B Plus TV Stick from here or from here. To flash firmware on this box via AMLogic USB Burning Tool read this article. Download previous firmware from here.
Archive name: mk808bplus_rtl8723bs_20150515_8Gflash HKW_r1
Image: mk808bplus_rtl8723bs_20150515_8Gflash HKW_r1.img
Archive size: 732 MB
Model: MK808B Plus TV Stick
Platform: AMLogic S805
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.