To control the EDs you need to get grbl up and running on your Arduino.
I used GRBL 0.8c which can be obtained from https://github.com/grbl/grbl
Scroll down to ‘Downloads’ and grab the 0.8c version. It is a precompiled hex file and can only be uploaded to the Arduino with an hex-uploader.
I used http://www.ngcoders.com/downloads/arduino-hex-uploader-and-programmer/
To avoid the ‘out of sync’ error you need to modify the baud rate at whiche the uploader sends to the Arduino from 19200 to 115200. See picture.
To modify the pinout of GRBL you need to get the sources from above link and manipulate the file config.h and recompile it afterwards, of course. There you are able to relocate the pins as you like. This might come in handy if you use another stepper driver board.
To recompile type in the shell: