Google has pushed out the 2nd Android 4.3 for this year on both the original Nexus 7 and New Nexus 7 (2013). You can unroot and do the updates yourself (which is time-consuming and you will have to re-root) OR you can simply grab rooted version of these firmwares as a ROM zip file and install easily using TWRP recovery.
So, grab them here!
Download Latest rooted stock ROM for your Nexus 7:
Latest Nexus 7 Android 4.3 JWR66Y ROM with root (This for original Nexus 7)
Latest New Nexus 7 Android 4.3 JSS15Q ROM with root (This for Nexus 7 2013 model)
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Nexus 7 Reference
You will need a rooted Nexus 7 to install all ROM/kernels.
First time to rooting and custom ROMs? Please see our Nexus 7 Root FAQ FIRST!