Download the Arduino IDE at: www.arduino.cc. Install and Open Arduino IDE Follow these steps to upload your sketch:
Connect your Arduino using the USB cable. (The square end of the USB cable connects to your Arduino and the flat end connects to a USB port on your computer.)
Upload code (copy and paste it to Arduino software.)
How to upload a code: Once you start Arduino software, delete the old code that is already there, and paste the new code you previously copied.
Choose Tools > Board > Arduino Uno to find your board in the Arduino menu. (You can also find all boards through this menu, such as the Arduino MEGA 2560 and Arduino Leonardo.) Please select Arduino Uno
Choose the correct serial port for your board. You find a list of all the available serial ports by choosing Tools > Port > ArduinoUno or comX or /dev/tty.usbmodemXXXXX. X marks sequentially or randomly assigned number. In Windows, if you have just connected your Arduino, the COM port will normally be the highest number, such as com 3 or com 15.
Many devices can be listed on the COM port list, and if you plug in multiple Arduinos, each one will be assigned a new number. On Mac OS X, the /dev/tty.usbmodem number will be randomly assigned and can vary in length, such as /dev/tty.usbmodem1421 or /dev/tty.usbmodem262471. Unless you have another Arduino connected, it should be the only one visible.
Click on the little "Upload" right arrow on the left side.