Download latest Android KitKat 4.4 stock firmware for Uhappy UP620 smartphone from here or from here.
Firmware image file: 20141202_e2709v92_jbla178_qhd_up620
Model： Uhappy UP620 smartphone
Image file size: 415 MB
Platform: Mediatek MT6592
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.