Plug the Arduino Uno into your computer.

Open Arduino IDE if you don't already have it open.

Select File → Examples → 11.Arduino ISP → Arduino ISP. This will open a new window with the example sketch. Work in here for the last few steps.

Select Tools → Programmer → Arduino as ISP

Select Tools → Board → Arduino/Genduino Uno

Select Tools → Port → Select the COM port that shows up. If none show up, plug the USB cable into another USB port on your computer and try again.

Hit the upload button.

Lights should flash on the Uno and Melzi