Here's how to prevent new cookies from being installed and how to delete existing cookies. The exact procedure depends on which browser you are using.
Internet Explorer
To prevent new cookies from being installed and delete existing cookies:
http://windows.microsoft.com/en-GB/internet-explorer/delete-manage-cookies
Firefox
To prevent new cookies from being installed:
https://support.mozilla.org/en-US/kb/enable-and-disable-cookies-website-preferences
To delete existing cookies:
https://support.mozilla.org/en-US/kb/delete-cookies-remove-info-websites-stored
Google Chrome
To prevent new cookies from being installed and delete existing cookies:
https://support.google.com/chrome/answer/95647?hl=en
Safari
To prevent new cookies from being installed and delete existing cookies: