You need a program that makes the picture smaller (less pixels), there is a free program out there called "IrfanView", make a search for it in Google and once you open a .jpg file you go to the toolbar and under "Image" click on the "resize" option and then input the values necessary (size) to be able to upload to this site, you must then "Save" this file in order to copy it to the server, you can also use Adobe Photoshop if you have it already on your computer, but IrfanView is a really good program and it is "free".
By replying to your message I am doing the same thing someone else did it for me a few years ago, it was so frustrating not kowing how to do these things. Hope this gets you a little closer to be able to input the pictures, good luck!