S5 Elite Lite ROM is based on Android 4.4.2 Kitkat and it gives your Galaxy S3 I9305 look of Galaxy S5. As Galaxy S3 I9305 is not yet received Android 4.4.2 Kitkat update and there is a report saying that it was planned to update to Android 4.4.2 Kitkat and however official dates was not yet revealed, so till then you can install S5 Elite Lite ROM to update Galaxy S3 I9305 to Android 4.4.2 Kitkat.
Make sure your device is Galaxy S3 I9305. Check in Settings > About. Enable USB Debugging on your device from the Developer Options Make sure your device is rooted and has latest Custom Recovery installed. If not go here.
Procedure to update Galaxy S3 I9305 to Android 4.4.2 Kitkat firmware using S5 Elite Lite ROM:
Download S5 Elite Lite ROM and transfer root of your device storage. Power off and enter into Recovery Mode. To do so press and hold Volume Up + Home + Power button simultaneously. From recovery menu, perform wipe data and cache options. Select “Install zip from SD card” and choose the ROM.
Now again perform full data reset and wipe cache and dalvik cache. Go back to main menu and select reboot system now. Once the device boots up you are ready to experience Android 4.4.2 Kitkat on Galaxy S3 I9305 via S5 Elite Lite ROM.