How to Clear Cookies & Cache on Browser and why
This is a pretty concise guide on clearing your cache no matter what browser you use: http://kb.iu.edu/data/ahic.html.
Basically your computer (in an attempt to make things faster for you) keeps copies of things (image and files, for example) on your computer, and the next time you request one of those things instead of getting it from the internet it gets that local saved copy. In this case you don’t want the saved copy, you want the new one from the internet. That's what clearing your cache does... it deletes all the local copies of things that your browser keeps around.