First of all that is waaaay too large of a photo size to be using…that would be if you wanted to print it in a full color ad, brochure or magazine. The web and all computer monitors are not capable of displaying an image that size or DPI (dots per inch, aka resolution).
So first you’ll need to resize it to be smaller in pixels so that it fits on your page given your Theme’s dimensions for the content area, and lower the dpi to 72. You’ll need some photo manipulation software such as Photoshop (or any of the free alternatives like GIMP). Some have a setting called “web resolution” or “web optimize”.
Also check your Media settings under Settings >Media – that’s where you have three sizes you can specify that WP will create when you upload a photo – you’ll want to be sure that your “Large” size is set to be as large as your theme will allow, no larger.
