Step 1: Download USBtinyISP driver software from Adafruit.com. Install the driver for the USBtiny device. Then, insert the new Atmega328P-PU chip on the DIL socket of Arduino board. Connect the USBtiny device to Arduino.
Step 2: Go to Tools-Board-Arduino UNO
Step 3: Programmer- USBtinyISP
Step 4: Tools- Burn Bootloader
It takes less than 1 minute to burn the Arduino bootloader to your new Atmega328P-PU chip.