There are two ways in which a website can recognise that you're not 'new'.
Firstly, every time you connect to a website your 'IP address' is forwarded to that site. (That's necessary so that the site knows where to send its data to). Most internet service providers use 'dynamic' IP addresses, which are allocated every time you log on. So, to get a new IP address, all you have to do is to disconnect from the internet and then re-connect. If you're in the minority of people who've got a 'static' IP address you'll need to use a proxy server to effectively change it. See my post here:
http://www.theanswerb...y/Question958319.html
However it's more likely that the site knows that you're not really 'new' because it's placed a 'cookie' onto your computer,which identifies you when you connect to that site. Deleting that cookie will convince the website that you're a new visitor to the site. If you're using Internet Explorer, see here for relevant information:
http://support.microsoft.com/kb/278835