The HESI is pretty simple if you give it about a week of brushing up on all the subjects they will be testing you on. I got the Hesi PockPrep app (purple and white and about $14 I believe) and I think that was one of my favorite study tools! I also watched crashcourse anatomy videos on youtube, there are about 40 of them. Start on lesson 1 and just work your way to the end. They were entertaining and touched on all anatomical areas. Introduction to Anatomy & Physiology: Crash Course A&P #1 - YouTube
I also got this book and read through it all and made flashcards. Admission Assessment Exam Review, 4e: 978 323353786: Medicine & Health Science Books @ Amazon.com
The vocabulary, math and grammar
sections were excellent in this book and really related to everything on the actual exam. A&P, Biology and Chemistry were well covered as well, but I think you need to find some outside resources for those subjects in addition to what's covered here to really nail those sections. If you just use this book and the pocketprep app you should be fine though.