how can a pixel in a bitmap can be deleted?

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C++

i m decreasing the resolution of a bitmap. i found a method on a site which is as follows

Average the values of all surrounding pixels, store that value in the choosen pixel location, then delete all the surrounding pixels.so a 4*6 matrix becomes a 4 x 3 matrix.

i am accessing pixels by this code

for(int y = 0; y < bmp.bmHeight; y++)
  {
      for(int x = 0; x < bmp.bmWidth; x++)
      {
          COLORREF rgb = dc.GetPixel(x, y);
          BYTE r = GetRValue(rgb);
          BYTE g = GetGValue(rgb);
          BYTE b = GetBValue(rgb);
          dc.SetPixel(x, y, RGB(r,g,b));
      }
  }

tell me how can i delete a pixel?