Problem with upload and download file

I have a problem with replacing the file with a newer one
when I upload a file via silverstripe and replace it in my website, everything in the view works perfectly.
But the problem occurs when the page is published. When my friend clicks a link, he gets the older version of the file

Can you provide a bit more info:

Version of SilverStripe?
How is the image associated with the page?
Have you checked to see if the newly uploaded image is published?