Ah, the joys of owning a Nexus device. In what has to be some sort of record, Jelly Bean ROMs for the GSM and Verizon Galaxy Nexuses have been released and are ready to flash. And thanks to the Nexus being a dev device, getting the builds up and running is actually extremely simple.
For the GSM variant, just download the ROM, do a full wipe, and flash the ROM via Clockwork Mod Recovery. A root fix and updated radio can also be flashed via CWM. If you have the Verizon version, do a full wipe, flash the ROM, and flash SuperSU.