Just download the Firmware from below or click on this link: dl1smf_keyer.zip
Unzip the file to the location where your usual Arduino Sketches (C++-Projects) are stored or another convenient place. The configurations soley takes place in the files pins.h and settings.h
The entries in pins.h most probably only need to be changed if you change the board-layout to something more convenient for you.
You however should keep in mind that if you change the pins you can not choose them arbitrarily. For example: To keep the ability of the keyer to wake up on a press on either side of the morse-key both connectors (dit/dah) need IRQ-capabilities.
The options in settings.h have speaking names and will be documented better as time permits. If you plan to use Anthony's (K3NG) firmware, you must match his pin-settings-file to the hardware-pins used by this keyer-board. Look into this' project pins.h.