How do I switch stores

The iTunes Store in a country is intended only for use by that country's residents, and only while they are in the country. To use the iTunes Store in a country you need a credit card (or other card type if acceptable in a country) issued in that country, billed to an address in that country, and also be physically present in that country when using the store. You are also restricted to waiting 90 days between country changes.

E.g., "The iTunes Service is available to you only in the United States, its territories, and possessions. You agree not to use or attempt to use the iTunes Service from outside these locations. Apple may use technologies to verify your compliance. - http://www.apple.com/legal/itunes/us/terms.html#SERVICE"
App Store Frequently Asked Questions (FAQ) - http://support.apple.com/kb/HT2001 when using iTunes --> "To change countries, scroll to the end of the iTunes Store home page and click the flag indicating the current country. To choose a different country, click the appropriate flag."
iOS: Changing the signed-in iTunes Store account - http://support.apple.com/kb/HT1311

According to the document, since you live in the US you can only use a US account and you can only use that account while in the USA. If you want to use the store in another country you have to set up a billing address with credit card in that country and be present in that country when using that country's store. You also won't be able to switch countries more than once every 90 days.