In both cases use the "Download Zip" button on the right.
For some spec. boards a spec. dir in the ArduinoAddons directory in the Marlin dir needs to be copied to the arduino environment. <arduinohome>\hardware\
Start the arduino IDE.
Select Tools -> Board -> Arduino Mega 2560 or your microcontroller
Select the correct serial port in Tools ->Serial Port
Open Marlin.pde or .ino
Click the Verify/Compile button
Click the Upload button
If all goes well the firmware is uploading
1. Install the latest non-beta arduino software IDE/toolset: http://www.arduino.cc/en/Main/Software
3. In both cases use the "Download Zip" button on the right.
4. Some boards require special files and/or libraries from the ArduinoAddons directory. Take a look at the dedicated [README](/ArduinoAddons/README.md) for details.
5. Start the arduino IDE.
6. Select Tools -> Board -> Arduino Mega 2560 or your microcontroller
7. Select the correct serial port in Tools ->Serial Port
8. Open Marlin.pde or .ino
9. Click the Verify/Compile button
10. Click the Upload button. If all goes well the firmware is uploading