Ok so I've finally made the plunge into the murky waters of Linux from a lifelong stint in Microsoft-land, and although the culture-shock is strong, the allure of almost-complete control of the code I use, combined with the newness of this open kernel has definitively made me a believer in all things Linux.
That said, I must brave the well-known snarkiness and general upturned-nosed forums of the said Linux forums to ask a question that will no doubt be looked upon as dubious in integrity, and/or redundant to the point of unbelievability due to its ubiquity. I have, for the record, looked for a good 2 hours in this, and other Linux-oriented forums and tutorial websites, and have yet to see a simple, step by step guide that answers my question.
So please, if I am making a huge mistake by reposting this question because of it being answered multiple times in an assumed well-made response elsewhere, point me to this response, so I don't bother anyone. I truly cannot find a decent answer to my particular conundrum.
I am currently running Ubuntu 16.04 on an Acer Aspire V3, with a 64bit processor and half a terabyte of space. I don't want to reinstall Ubuntu, as I've downloaded many packages and tweaked the OS to my liking; Also converting my OS back into an ISO would be out of the question because I don't want to do that.
I also already have a working live USB of Kali (previously checked and is working).
My Gparted system breakdown looks like this (screenshot):
Screenshot from 2016-05-26 23-01-44.jpg

What would be the easiest way to repartition my HDD and install Kali alongside my Ubuntu OS? I'm using Grub2 as a bootloader. I'm sure I'm forgetting more pertinent information; I'm not doing so on purpose so if I am, please tell me what to provide, as well as how to provide it, and I will as soon as possible.
Thank you so much in advance!

-Aquashift