Xbox gamertag error

That error code suggests that there is already a gamertag attached to it. You can only have one gamertag per Microsoft Account.

support.xbox.com/.../error-code-80154013

The recommended fix for this error is as follows: Delete your gamertag, clear your cache, and recover your gamertag

For further information on this error please see
support.xbox.com/.../error-code-831188fe

To resolve this problem, choose another gamertag.

Xbox Live gamertags are unique and personal. We protect this uniqueness by not allowing the same gamertag to be created with different spacing. For example, if “Coolgamertag” is taken, that means “Cool gamertag” and “cool gamer tag” are also taken.

Source: https://support.xbox.com/en/help/errors/xbox-360/error-code-80154303

What type of error are you getting when trying to change his gamertag?

Here is a link to instructions on different ways to change the gamertag.

Instructions on how to change gamertag

If you followed the instructions on how to change the gamertag from this link and are getting an error message we would need to know what the error message is that you are getting.

Error 80154303 occurs when changing your gamertag on Xbox Live

You see the following error code when you try to change your Xbox Live gamertag:

80154303

This may mean that the new gamertag you’ve chosen is already in use or unavailable.

Solution

To resolve this problem, choose another gamertag.

Xbox Live gamertags are unique and personal. We protect this uniqueness by not allowing the same gamertag to be created with different spacing. For example, if “Coolgamertag” is taken, that means “Cool gamertag” and “cool gamer tag” are also taken.

If you keep experiencing the problem, contact Xbox Support.

Gamertags are used on other services,not just xbox live.You will need to pick another gamertag i'm afraid.