Don’t worry, your new image really is there, and it’s likely that everyone except you is seeing it. This is an unfortunate consequence of how browsers cache (and expire) images.
Try opening a Private/Incognito window in your browser and viewing the page. You can also restart your browser, manually clear the cache, or just wait a bit for your browser’s cache to expire. You could also try viewing your website using a different browser, different computer, or mobile device.
Additionally, our CDN caches your images, and it can sometimes take a few minutes for the cache to be purged.