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:

http://help.apple.com/safari/mac/8.0/#/sfri11471