Then make sure you have downloaded the gapps and moved it to your SD card.
1. Use the flash tool or cmd to flash the phantom kernel via fastboot.
2. Then flash the system.img again via flashtool or fastboot.
3. Now flash the userdata.img via fastboot.
4. Now boot into recovery and flash the gapps.
5. Reboot and enjoy your kitkat.
Optional. Wipe data and dalvik cache if you want to.
Flashing system and boot via flashtool.
1. Click the thunder button.
2. Choose fastboot.
3. Make sure you have booted your phone into fastboot mode.
4. Choose select kernel to flash and then choose phantom kernel. (change file type to img in the drop down list box).
5. Choose select system to flash and follow the same.
Flashing userdata via fastboot.
If you don't have the fastboot files on your laptop,
Follow from step 1. Else skip to step 2.
1. Copy the userdata.img to x10flasher lib.
2. Hold shift and right click on an empty space in the folder and choose start command prompt here.
3. Type the following code.
fastboot flash userdata userdata.img