How to Change your country in Google Adsense

Can anyone tell me how to change my country on Google's Adsense Account?????

I have shifted to US from Pakistan a couple of months ago. Now that I could find a little bit of time, I checked my Google Adsense account and tried to change my address. To my surprise, the country field was disabled there. I went to Adsense Help and there I read that I have to send an email to the adsense team in order to change my country. But at which address? I couldn't find any customer support email address on their site.

Help Required...