Cookies can be deletes easily:
Internet Explorer: right click on Start> explore> Cookies> click on the box to the right of word 'Folders' and choose Tiles for view. now you can see where the Cookies come from. You will have to at least enable First Party Cookies- those are from the site itself. Most sites require this. But Third Party Cookies can be either blocked or set to Prompt.
To set Cookies in IE: Internet options> Privacy> Advanced button> check 'override automatic Cookie handling'> check 'allow first party'> check 'prompt for third party'> OK> Apply OK.
If you don't selectively delete Cookies, chances are you have many> Internet Options> General tab> Delete files> Delete Cookies.
Firefox works differently: It is harder to selectively set Cookies, but easier to see and delete them: Tools> Options> Privacy tab> You can set to 'always allow' which is what I have, the choose to keep 1. until they expire, 2. until you close Firefox or 3. always ask you. I have #1, but because I call up so many sites, I check my Cookies frequently and delete.
You can also find Cookies in hidden files.