Background image not updating

https://www.happyhealthypets.net

I’m having an issue getting the updated version of the repeating image at the top to show up. They’re pink circles now but I changed the colors and uploaded a replacement file to my server in the same spot with the same name as the previous one. I checked the CSS and the image is pointing to the right place as far as I am aware (images/background.gif). Any ideas on why it’s not showing up? I tried it on another browser so the cache isn’t the issue, I don’t think.