Upgrading to Windows 10 from 8.1 in Bootcamp

Hi,

I just recently installed windows 8.1 on my retina macbook pro 15 using bootcamp. I now have a windows 10 upgrade iso on a usb and a product key. Im wondering now how to perform the upgrade. Do I do it through the windows partition, or on the OS X side using bootcamp? Also, if I do it through the windows side, do I run the risk of having the upgrade wipe the OS X partition or will it stay within the windows partition? Mind you, I'm not very tech savvy, so please use as much detail as possible.

Thank you,