how to change RGB to grayscale image processing with delphi??
please give me a source code with delphi programming.

That's a tall order. You'll have to google for some image processing components.
You might want to take a look at ImageMagick.

If you just want to convert an RGB tuple to a single grayscale value, it is something like:

function toGrayScale( red, green, blue: cardinal ): cardinal;
  result := trunc( (red * 0.3) + (green * 0.59) + (blue * 0.11) )

Good luck.