Please tell what precisely happens on your screen when you try to upload.
Also have you resized the photo before uploading it?
FAQ My photo is too large to upload. How can I reduce it?
You may edit your photo in a photo editing program like Photoshop and reduce the length, and then save it as a jpeg using a compression level such that it is less than 300kb. If you do reduce the length of the photo, you probably will want to sharpen your photo using Unsharp Mask.