Resizing (in PS)
IMPORTANT; Save your original image and any editing you have done BEFORE resizing. Resizing is a destructive edit (you lose detail) so you need to keep a "best" copy somewhere safe.
In Photoshop (and, probably, elements) go to Image > Image size
The window that opens will show you the current image size - 8,256 x 5,504 by 72dpi in this case.
If you want to change the DPI do that first - simply type the new number over the 72 (it will be different for your image).
Then if your image is landscape change the width to 1600.
If your image is Portrait (or square) change the height to 1200.
Phososhop will adjust the other measurement to keep the image ratio
In this case after I entered 1600 Photoshop set the width to 1,067. The resolution was unchanged in this case.
Finally use File > Export > export as (usually a JPG image). I add _1600 (or _1200) to tell me the image has been resized e.g. Banger racing _1600.JPG
DO NOT save over your original filename as this destructive edit cannot be undone if you do that.