how to uninstall unojoy arduino mega

Hi, I'd like to know how to uninstall the unojoy program from my arduino board, I'm a beginner and I'm learning now, my arduino is Mega 2560 16u2

Every time you upload a sketch to your Mega, the previous one is deleted. So to "uninstall", you only need to upload a new sketch.

Ah, scratch that. I see that UnoJoy is something you install onto the ATmega16U2 chip on the Mega. You can find the standard firmware for the ATmega16U2 at {Arduino IDE installation folder}/hardware/arduino/avr/firmwares/atmegaxxu2/Arduino-COMBINED-dfu-usbserial-atmega16u2-Mega2560-Rev3.hex. You should be able to install that file the same way you installed UnoJoy.