The first thing you need is an empty SD card.Then downloading the 4.4 kitkat system files from the following link:

KD Dual-core Head Unit:!YUFUXBYQ!sBLzETgn10tcpeFG5675RE295rSy4a18aZ2FJucPkWk
KD Quad-core Head Unit:!JYc3GBpa!pb0UVJj3ggpdWNLGJetZCUrSbZSzme6Tscc62rRnuEU
GS Dual-core Head Unit:!kFl1RBLQ!nzNelC8PCMjDE1-gNG76YZsvCGiun7QLtj7i-bEsy7M

After downloading,please unzip it and copy the files into the empty SD card.
Then turn off your car,turn off the radio, insert the SD card into the GPS slot, then use a thin sticker to long press RST hole on front panel,such as touch pen,then turn on your car ,turn on the unit.Then you will enter the recovery mode,when you are in the recovery mode, short press the RST button is for switch, long press RST hole is for start the update, pls choose to update the unit from the SD card files.

Following is the instruction vedio you may need for reference.