Carol, the pixels is the size. If it says 3600 x 3600 then that is 12 x 12 inches. Once you change the 3600 to 2400 it becomes 8 inches instead of the 12 inches. You should be able to see the inches size when you view the JPEG in your PSE program - you click Image and then resize.
Are the JPEG images what you have created or the preview of templates ? Are you resizing your finished layouts?