Installing KitKat on rooted Jelly bean Nexus 7
If all else fails, you can flash those images in Fastboot. Remember to make a Nandroid and back it up somewhere safe - this will wipe your device.

If you're on Windows or OSX, you'll need to install Fastboot through the Android SDK. It's part of the "Platform Tools" package. If you're on Linux, you can usually install fastboot through your package manager.

Additionally, Windows needs ADB and fastboot drivers for your device.

First, you need to boot your device into fastboot/bootloader mode by holding down the Volume Down button while powering on. You can also use an expanded reboot menu or ADB: adb reboot bootloader.

Second, unzip the file you've downloaded. Remember where you unzipped it to.

On Windows:


Optional: Add the path to your Android Platform-tools (ADB and Fastboot) to your PATH environment variable.
Open an elevated Command Prompt. (I think elevating it was necessary)
In the Command Prompt, navigate to the unzipped Android files.
Type flash-all.bat and press Enter.

If this doesn't work, you will need to specify the location of the fastboot.exe file by modifying the PATH=%PATH%... line in the flash-all.bat file.



On Linux or OSX:


Unzip the downloaded .zip file.
Open a terminal.
Navigate to the unzipped files in the terminal.
Type ./flash-all.sh and press Enter.