shimidan:
but no enough info about changes had to do in ArduinoISP sketch. For example, It is not clear frequancyof programmer or target must be entered in the sketch.
That's because no changes are necessary. Just leave the ArduinoISP sketch alone. It's configured correctly just as it is when Arduino provides it.
shimidan:
Could anyone tell what exactly to do for burning UNO with MEGA 2560?
I think it's fairly well documented in the tutorial already, but here you go:
Connect your Mega 2560 to your computer with the USB cable.
Tools > Board > Arduino/Genuino Mega or Mega 2560
Tools > Port > select the port of your Mega 2560
File > Examples > 11.ArduinoISP > ArduinoISP
Sketch > Upload
Wait for the upload to finish successfully.
Unplug the Mega 2560 from your computer.
Wire the Mega 2560 to your Uno following this diagram:
Connect your Mega 2560 to your computer with the USB cable.
Tools > Board > Arduino/Genuino Uno
Tools > Programmer > Arduino as ISP
Tools > Burn Bootloader
Wait for the Burn Bootloader process to finish successfully.