You can't change your real IP address but you can change the address which the site you're trying to access actually sees. Simply use a free proxy server. It's easiest to configure if you're using Firefox:
http://www.mozilla-europe.org/en/firefox/
Look through this list to find a possible proxy server:
http://nntime.com/proxy-country/
Under the 'IP Address' column, you'll see a 'dotted quad' (such as 147.213.82.11) followed by a port number (such as 80). Note down the details of the proxy you wish to try.
In Firefox, go to Tools > Options > Advanced > Network > Settings. Click alongside 'Manual Proxy Configuration'. Enter the dotted quad into the 'HTTP Proxy' field and the port number into the 'Port' field. Click 'OK'.
Try accessing this website to see which IP address is being forwarded to any site you visit:
http://whatismyipaddress.com/
Some proxy servers probably won't work but many will. (I've posted this so that AB sees my post as coming from Bratislava, so that's one proxy server which is definitely working!).
Chris