To burn bootloader to Arduino MEGA 2560 using Arduino Uno as ISP, connect Uno & MEGA as shown:
PC is connected to Uno.
- Program Uno as ArduinoISP
> Select board of Uno
> Select programmer of AVRISP mkII
> File > Examples > ArduinoISP > ArduinoISP
- Now we are going to program MEGA, the Uno act as Arduino as ISP.
> Select board of MEGA
> Select programmer of Arduino as ISP
> Tools > Burn Bootloader
As shown in this video: