Android 4.3 is has been available for a little over a week (longer depending on when you read this article). If you are currently rooted, you will lose root by taking the Over-The-Air (OTA) upgrade. However if you want to keep root and not lose all your apps and data, there is a rooted Android 4.3 file that you may use and keep root plus your apps and data. This is stock Android not a custom ROM. If you want to install custom ROM, there are many threads that provide information on this. This article only pertains to stock Android 4.3. Continue reading...
XDA Developers have a thread where you will find this rooted stock Android 4.3 (JWR66V). This is for the original Nexus 7 not the new version that came out in July 2013. In order to flash or install this, you must currently be rooted and you must have a custom recovery installed on your Nexus 7. If you are not rooted or have a custom recovery, you must do both before flashing/installing this. If you need to know how to root your current Android version (not 4.3) and install a custom recovery, this thread provides instructions how.
If you have any issues, post your problem and explain in detail what you did. There are people always willing to help you.
Disclaimer: Anything you do to your Nexus tablet is risky. You assume all risks. TabletConnect is only providing information that points to these threads and is not liable to any damage you do to your device. Please do not post questions or issues on these methods. You should post them directly to the thread.