Let’s say you have an image which you want to change the size of. In most cases, you want to make the image smaller, but resizing an image to be larger can also be done. In Photoshop, the steps are very easy:

1. Open the image (File > Open…)
2. Click Image > Image Size…
3. In the section called “Pixel Dimensions,” enter a new value for Width or Height. The drop down boxes allow to you to specify if the values will be in Pixels or Percent. So, for example, if you want to resize the image by half, pick “Percent” and type in “50” for Width & Height.
4. There will be a checkbox near the bottom called “Constrain Proportions.” This will lock with width and height to maintain the same ratio as the original image. Generally you want this checked so that your image will not distort or appear “stretched.” If unchecked, you can change width & height independently to any value.

That’s it! Now you can re-save the image. The method described above works in previous versions of Photoshop too, such as CS5 and earlier.