Here's a link to the guide I followed to flash my H8 with the open source code. I put the dual firmware on mine and have since moved over to a carbon fiber frame (will post about that later). Flashing was easy but my quad drifts quite a bit, so its hard to control. I'll have to look into adjusting the levels, but that'll be a new adventure for me.
https://dronegarageblog.wordpress.com/2016/01/06/eachine-h8-open-source-firmware-with-acro-mode/