It is likely because your browser is cacheing (storing) the old image instead of showing you the most current.
There are a few tricks to make sure your new image is loaded:
1. Press CTRL + F5 while on your site.
- This will clear your browsers cached memory (clear the cache) and reload the latest changes.
2. When replacing an old image:
- select 'Edit Content' from the Control Panel
- click 'Browse' next to the image you want to update
- select the new image
- select 'Apply Changes to this Page'
** you do not have to delete the new image - when you select the new image it automatically replaces the new image
** do not check the delete box of the old image and upload the new image, your new image will be deleted
3. Set the browser so it will show the most recent images.
- To do this in Internet Explorer:
- select 'Tools'
- select 'Internet Options'
- select 'Settings'
- select 'Every Visit to the Page' under Check for Newer Version of Stored Pages
4. Refresh the page on your browser when viewing the page with the new image.