You have to make the picture smaller on your computer and upload that smaller picture to your website. That's what I did. My pictures open up in Microsoft Photo Editor. I go to "Image" and then click on "resize" and make it smaller that way. Just be sure that when you save the picture, you don't override your original. I just put a "sm" in front of what ever the picture name is so I know it is the small one and save it that way. Hope this helps.
The picture below in its original size would fill your whole screen and more!