Download and install the latest version of the Arduino IDE.
Download the pre-configured version of Marlin from the smartrap github, extract it, open it in the Arduino IDE, select your board and com port in the menus, and hit the upload button.
If you need more detailed help, just look up how to program an Arduino. Ramps 1.4 is just a shield and is dumb. There's nothing on the actual RAMPS board to flash...it's all in the MEGA board beneath.