[help] when i ota update it goes down to 3.2.8 not higher i want 4.5.5.1

I would like to update my kindle fire hdx thor to 4.5.5.1 to improve battery life if you could show me how to update from 3.2.8 to 4.5.5.1 I have enabled ota and uninstalled safestrap and i don't what to do next.

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