I agree that the best and easiest option for you is to use Calibre with Apprentice Alf's tools and convert to azw3. However, if you actually want to read epubs on the Paperwhite you can install KoReader. This does not "ruin" your Paperwhite but does jailbreak it and is probably getting away from the "easy way" as per your initial post. Another option, installing Duokan, is similar, and not encouraged.
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