Each time you visit a website your browser remembers / stores parts of the website so it can load the page faster next time you visit that website. This is called Caching. Sometimes caching can prevent you from seeing the latest version of the website e.g. new images / content that have been added since the last time you visited.
To get the latest version of the webpage you are visiting you can bypass your cache and force your web browser to retreive the latest version of the page you are on.
Sometimes bypassing your cache does not work due to a number of reasons. The next thing to try is clearing out your entire browser cache.
Clearing your cache is a good way to ensure you are seeing the latest version of all the websites and pages you are visiting.
Depending on what internet browser you use, e.g. Google Chrome, Mozilla Firefox etc, there are different ways you can clear out the cache so you can see the newest version of the web page you are on.