Q: change of country

What problems are you having ?

Moving countries and updating your address on your account (if you are now in the US then you can only use the US store) will not remove any of your downloads from your devices and/or computer's iTunes library, you will just lose the ability to redownload them (though you should have a copy of all of your downloads on your backup of your library anyway).

1. Click here and follow the instructions to change the iTunes Store country.

2. No.

(123069)

You don't need a username, you just have to update the details on your existing account.

There are some steps on this page for how to do it : Change the country of your iTunes Store, App Store, iBooks Store, and Mac App Store account - Apple Support

If you can't change the country (e.g. if you have a balance on your account or outstanding season passes) : Can't change the country of your iTunes Store, App Store, iBooks Store, or Mac App Store account - Apple Support