Probably your browser settings.
Open up Internet Explorer.
Goto the "Tools" option at the top of the window and select "Internet options"
On the "General" tab you will see a section called Temporary internet files which contains a "Settings" button.
Click on it and here you will find "Check for newer versions of stored pages" with four options. Select the "Every visit to the page" this will updated all your stored files of each website you visit everytime you visit it.
I hope thats makes sense, I'm rubbish at explaining things I know about to others.