Changing the password:

Step one -

Sign into the account by clicking this link;

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Once you have securely signed in, click this link and change the password.

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Changing verification/security proofs:

Step two -

Please click this the link below to change the mobile number to the given account. Make sure this number you'll have you access to, it's vety important.

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Every security proof is important so you're going to need to change your email to: (an alias, this is a secure account that you own that only you have access to)

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Once you've added all your information (email address & mobile number as well as extra security information) and verified them, remove the previous users details. Make sure you select "use as primary".

Some times, if the previous account holder added there mobile number, you're going to need to contact them letting them know that you're going to need a 6-7 Character code.

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Changing/Deleting Billing Options

Step three -

If there any other billing options visible, you can either replace them with your own OR just delete them. Personally, I'd use my own for security reasons. Click this link to see if there are any options:

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Removing the account off other consoles

Step four -

You're going to need to remove the account of other consoles (Xbox 360 & Xbox One) this is also important, please click this link to remove off any other Xbox One consoles;

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This next link is to help with future Xbox 360 Sign-in attempts, it will require a password to sign in from now on. Thus, removing it off there console.

[ Register or Signin to view external links. ]

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Extra steps -

Although once you've done the following steps and don't feel comfortable with the amount of security, you can also use a 2 step verification method. You don't need to do this however it's definitely helpful. Please turn it off if it's on already.

Other details - underneath "close account" there is also an option to "remove all trusted devices from acsossiated account" don't forget to do that!