Google has start rolling out Android 4.4 KitKat updates for Nexus 7 and Nexus 10. The easiest way to update your Nexus devices to Android 4.4 is to download it from the OTA link. It is easy to upgrade your phone from the OTA upgrade. Here, is how you can do it:
Once you have downloaded the OTA link, transfer the files on your desktop under the folder named Android. Then download the ADB/Fastboot files and the USB drivers for Windows,
Now dig out the ADB/Fastboot Zip file contents into your Android folder.
Now turn on the Bootloader mode of your Google Nexus 7 tablet. Select the “Recovery” option and press the power button. Now reboot your phone in the “Recovery” option.
Once your Nexus 7 device is booted, choose the update from ADB. Now connect your device to the computer and open the Android folder on your desktop. Now copy paste the following
./adb sideload update.zip
Now the file transfer will start and you can select the “Reboot system now” on Nexus 7.
Once you do that you will have the Android 4.4 KitKat update on your phone.