You can always reject cookies on your computer, tablet, or phone by changing the settings in your browser. Where you find the settings depends on which browser you use. You can opt out of cookies from Google Analytics here.
It is possible to opt out of some ad networks that share information across different networks here.
cookies that you have previously accepted can subsequently be easily deleted. If you use a PC with a newer browser, you can delete your cookies using the shortcut keys: CTRL + SHIFT + Delete.
If the shortcut keys do not work and / or you use a MAC, you must first find out which browser you are using and then click on the relevant link: