Browser programs are frequently updated to add functionality and address problems. If you are using an older version, you may not be seeing websites the way they are meant to be displayed, and there could also be security issues.
To check what version you currently have on your computer, open the browser program, go to the toolbar up top, click on "Help," and then click on "About [the name of the program.]" The easiest way to update your web browser software is to download the update over the Internet. You can download the update for free by going to the company's website, and clicking on a link that usually says something like "download now".