Many services cache site data to reduce the time it takes to load later. Also, Telegram often caches data, but this cache can be cleared manually.
You can refresh the preview cache using the bot @Webpagebot. First, you need to press the "Start" button or send the command /start.
Then send a link to the page whose preview you want to update. For example — http://nic.ua/.
If you want to refresh the preview of the same page once again, use the "Update preview again" button or the "Update with content" button.