Android 4.2 is rolling out to Galaxy Nexus and Nexus 7 devices. If you’re impatient, there’s a trick which worked for me:

• Go to Settings<
• Disable Wifi
• Go to Apps, then to All
• Find Google Services Framework
• Force Stop
• Clear Data
• Go back to Settings
• Enable Wifi
• Go to About phone/tablet
• Go to System updates
• Check now

Your mileage may vary.

Source: Gotta Be Mobile