If the book is on the device, press and hold on the cover and select "remove from device" from the pop-up menu. Either on the Carousel or on the Books tab. (If you're looking at the Cloud in the Books tab, downloaded books will have a check on them.) At least on the Fire HDs.
A forum community dedicated to Amazon Kindle owners, authors, and enthusiasts. Come join the discussion about publishing, audio, troubleshooting, models, styles, reviews, accessories, classifieds, and more!