Install OTA 4.2.1 update on stock N4 - The Easy Way!
First connect to WiFi and make sure you can access the web.
Next put the N4 into airplane mode.
Then go to Settings > Apps > All > Google Services Framework > Clear data
Take the N4 out of airplane mode and let it connect to WiFi.
After a few minutes, you will be prompted to install the OTA update.
If you are not prompted within 10 minutes, open the dialer and force a "checkin" by typing: *#*#2432546#*#*
After "checkin succeded" message, you should be prompted to install the update.