you must have already installed Chinese Firmware B120 or B118 !
by installing B118 Chinese Firmware there is a risk that your device may become unusable !
root not require !
you must have already installed TWRP Recovery or CWM Recovery!
copy FLY-UI on your external sdcard !
put your device in recovery mod ;
Wipe -> Advanced Wipe -> select : Dalvik Cache, System, Cache, Cust & Data ! ( equivalent to "Clean Install" )
Swipe to Wipe ;
Install -> select : Storage : External Storage !
Swipe to Confirm Flash !
Wipe cache/dalvik !
Reboot System !
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