1) Make sure the image you start with is larger in width than the size template, so that image doesn’t become blurry once it was resized.
2) Open both your original image that you want to use for the Post image, and open the Size Template file.
Then “select all” in the original image, and “paste” it into the Size Template file.
3) Next, you would want to resize the pasted image to match the width of the Size Template.
Then all you do is size that file to a new file name and upload it to your new Post.
NOTE: You can see how that image is a little blurry because the original image was smaller than the final size dimensions. You can also see how parts of that image must be cropped out in order to stay in the correct size dimensions.
