Google is rolling out Android 4.2.1 OTA to fix a minor December bug in the People app for Nexus 10 users. You can download and install the update manually on your device by going through the steps mentioned below.
To install Android 4.2.1 on Nexus 10 you should be running Android 4.2 JOP40C firmware. You can confirm the firmware version from Settings » About tablet menu on the tablet.
Install Android SDK to install drivers.
Download Android 4.2.1 OTA for Nexus 10. ( 07ac4f5d6c30.signed-mantaray-JOP40D-from-JOP40C.07ac4f5d.zip) and download Fastboot from here (Fastboot.zip).
Extract Fastboot.zip to a folder named as Fastboot in C drive.
Copy the Android 4.2.1 OTA to Fastboot folder.
Switch off device and boot into recovery.Hold down Volume Up, Vol Down and Power buttons simultaneously till the screen turns on. When Android logo with Red exclamation appears then hold Power button and press Volume Up key to find recovery menu. Select “apply update from adb”.
Connect device to computer via USB cable.
Open Command Prompt on your computer and type the following commands. Press enter after typing each command on Command Prompt –
adb sideload 07ac4f5d6c30.signed-mantaray-JOP40D-from-JOP40C.07ac4f5d.zip to flash the update.
When the update gets installed your device will reboot automatically.
Android 4.2.1 JOP40D is installed on your Nexus 10.