Install Samsung Kies on your PC or laptop:
http
/www.samsung.com/uk/support/usefulsoftware/KIES/JSP
Now plug your phone into PC/laptop with USB data cable.
You should see two new drives in Windows Explorer.
One is memory card, one is the built-in storage.
Open & position both windows side by side.
Drag and drop photos from built-in storage window in to the memory card window.
Bear in mind the above instructions are based on how I do it with my Sony Xperia & different drivers of course.
I've never owned a Samsung phone nor have I ever used the Kies software so forgive me if my procedure does not work for you.