I cant change my microsoft account on xbox 360

Hey!

Have you tired logging into your account on account.microsoft.com and changing it through the website?

You can also request a Request a call back from Xbox and see if they can better support you from their end

That is what the problem is you can not change the email to an email that is ALREADY a MS account email (Hotmail, outlook, live, msn) the best thing to do is sign into your current account at account.live.com/addassocid and either create a new (outlook.com)
email account or use an existing email non MS account like a Gmail, yahoo, ISP server email that is not already a MS account.

Hi there, have you waited 30 days since downloading the profile to the Xbox 360 console? If you made any changes and didn't re-download the profile, I don't think the 30 days cones in affect.

Note You also must wait 30 days after your gamertag is downloaded from Xbox Live before you can switch that gamertag to a different Microsoft account.

From here:
support.xbox.com/.../cant-change-microsoft-account-now

Im trying to change the pay method but i cant, i cant buy things with my microsoft account, helpª

It depends on what you're trying to buy.

Currently, you can't buy Xbox 360 backwards compatible games with Microsoft Account money on the Xbox One or on the website. But you can buy with Microsoft Account Credit on a real Xbox 360.

Some subscriptions like EA Access can't be paid with Account balance as well.

So in order to help you better, it would be necessary to know what exactly you want to buy with your Account balance.

support.xbox.com/.../cant-change-microsoft-account-now