Now click OK. Your image onscreen should look exactly the same. So, how do you know it has changed?
Choose View > Print Size. The image will be resized to the approximate print size that we chose: 6 by 4.5 inches. If you were to actually print the image it would print at this size, and if you save the image, the print size is generally retained with it (unless you use the Save for Web command to save the image). By changing the resolution of the image without resampling we have not changed the pixel data at all. You've only given Photoshop information about how you want the image to be printed.
