Duvet Covers - 5000 Pixels & Resolution

Hi everyone, I see now through pixels.com we are offering duvet covers right here on FAA. I also note that the image must have 5000 pixels on each side to be considered. Nearly all my pictures have this capability but I cannot upload them because they are way over the 25 mb limit. So how are folks doing this?

If I lower my resolution, it lowers the pixels and size of the photo and I also question the quality. Any image I have that is 5200 on one side is always over the limit. I am certain there are folks here who understand what you need to do, so please let me know. I use photoshop cs5.5 for my scans and uploads. Thanks