hi guys
can i used ft232rl instead of atmega16u2 in arduino board like mega2560 or other?
pls help to me....

You can use any USB-to-TTL-Serial converter you like.

any file in arduino ide must be change or not

The USB/Serial is outside of the Arduino IDE.
For FTDI, you only need the drivers from ftdichip.com
Which I think are also included in the IDE in the drivers folder, you need to point Windows to there when it sees the chip.