I'm copy paste this tutorial from forum.xda-developers.com :
The Nokia X owners may also want to keep their device up-to-date. So we thought of giving you a tutorial of how to upgrade Nokia X to Android 4.4 KitKat. With new version of android operating system on your device, you will have more benefit. Your device will have more feature, more secure, more fast performance, and more cool he...3x. But prior to telling you how to install Android 4.4 KitKat on Nokia X, let’s see what do you want in order to be able to perform the installation. You will have to download 4.4 KitKat Nokia X ROM. You will also have to root your Nokia X to prepare it for Android 4.4 KitKat upgrade. Discover how to root Nokia X and install Android 4.4 KitKat from here. Here are the download links of the files you want to update Nokia X to Android 4.4 KitKat. Just before beginning to upgrade your Nokia X to Android 4.4 KitKat don’t forget to backup your information, as contacts, text messages and the apps installed from Google Play Store who maybe lost when the installation finishes. Now let’s see how to update Nokia X to Android 4.4 KitKat :1. Install the ROM Manager on your Nokia X. Get it from Google Play Store, then install the clockwork mod recovery.
2. Connect your Nokia X to your PC employing the USB information cable. Copy the “ROM.zip” file you downloaded to the SD memory card.
3. Restart your device in the recovery mode using ROM Manager. As soon as in Recovery Mode, go to ROM Manager and select backup / restore to back-up your information.
4. From the Recovery Menu do a total data erase (including Delvik Cache). When completed, go back to Recovery Principal Menu and choose Flash ROM from SD Card. Navigate the location you copied the ”ROM.zip” file and follow the directions for installing Android 4.4 KitKat on your Nokia X. As soon as the installation is over, just reboot your Nokia X device, and here you go, you’ve just upgraded it to the new Android 4.4 KitKat
