How can I change from Apple store USA to Apple store Mexico

Apple policy states that you can use the store for the country of which you are a legal resident providing that you can provide a payment method for that country's store. If that is a credit card then it must be issued by a bank in that country with a billing address in that country.

I qualify for an account in Mexico and the US because I am a legal resident of both nations and can supply a credit card from the US for my US account and from Mexico for my Mexican account. To maintain the two accounts I use two separate Apple IDs, one for the US and the other for Mexico. I have authorized my Apple devices; Macs, iPhones, iPads and iPods, to use the content from both accounts.

To change your account from the US store to the Mexican store I would use the iTunes app. Sign into your iTunes account and view your Account information. First change the country/region in the information from the US to Mexico. Second, you may then change your payment method acceptable in the US to one that works for Mexico. The iTunes account is also the Mac App Store account.

Open the App Store then scroll down to the bottom of the window then click the flag icon to change the country.

Regarding payment method and location.

The Complete Guide to Using the iTunes Store | iLounge Article

"Although you can browse the iTunes & App Stores in any country without being signed in, you can only purchase content from the iTunes & App Stores for your own country. This is enforced via the billing address associated with your credit card or other payment method that you use with the iTunes Store, rather than your actual geographic location."