It is not possible to directly upgrade Nokia X.
Nokia X supports upgrades, but the updates have to come from Nokia. Once Nokia releases updates, a notification will be shown and you can update. You can also check for updates manually by going to settings>>about phone>>system updates.
so direct updates to kitkat or jellybean are not possible unless Nokia releases one. Nokia may not release Nokia X software on current android versions. So it is always going to be older android versions that you will have on Nokia X.
On the other hand, if you want to change the interface on Nokia X, you can install a different launcher on Nokia X.
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