How to change your location or country?

Scroll to the bottom of the iTunes window where you should see a round flag symbol. Click on it, locate the desired country and select it. Log in to iTunes Store using the Apple ID used in that country.

Change iTunes Store Country on an iDevice

1. Tap Settings;

2. Tap iTunes & App Stores;

3. Tap View Apple ID;

4. Enter your user name and password;

5. Tap Country/Region;

6. Tap Change Country/Region;

7. Select the region where you will be located;

8. Tap Done.

Also, see How to Change Your iTunes Store Account Location | eHow.com.

http://support.apple.com/kb/ht1311

See that link above, about a third to half the way down the page ("Change your iTunes Store country"). Note that to use another country, you must have a form of payment native to that country, with a billing address in that country.