Here i will teach you how to change your gamertag for free just follow my steps enjoy guys!


Steps:

Scroll right to Your Information and select Account Security.
Select Microsoft account (Your Microsoft account is your Windows Live ID.)
Do one of the following:
If you already have another Microsoft account, select Yes.
If you don't have another Microsoft account, go to accounts.live.com and click Sign up. After you have another Microsoft account set up, select Yes and continue with the next step.
Enter the password for the Microsoft account that is currently associated with your gamertag and select Sign in.
Enter the email address and the password for the new Microsoft account that you want to associate with your gamertag, and then select Sign in.
Select Yes, change to change the Microsoft account associated with your Xbox LIVE account.
Select Update Contact Information to update your contact information or Done to finish.
Notes

If you try to switch your Xbox LIVE gamertag (or Xbox Music tag) from one Microsoft account to a different Microsoft account that's already linked to another Xbox LIVE gamertag, you'll get the following error message:
The Microsoft account (or Windows Live ID) youre switching to is already linked to another Xbox account.

Before you can switch your gamertag in this case, you must first remove the existing gamertag from the Microsoft account you want to use. Here's how:

Consider the following scenario:
Gamertag A is linked to Microsoft account 1.
Gamertag B is linked to Microsoft account 2.
In this scenario, your gamertag is Gamertag B, and you want to move it to Microsoft account 1.

At accounts.live.com, create a new Microsoft account. You'll only need this account as a temporary means of moving your gamertags.
Example:
Gamertag A is linked to Microsoft account 1.
Gamertag B is linked to Microsoft account 2.
Microsoft account 3 is free.
Switch the gamertag that's linked to the Microsoft account that you want to use to the Microsoft account that you created in Step 3.
Example:
Microsoft account 1 is now free.
Gamertag B remains linked to Microsoft account 2.
Gamertag A is now linked to Microsoft account 3.
Switch your gamertag to the Microsoft account that you want to use.
Example:
Gamertag B is now linked to Microsoft account 1.
Microsoft account 2 is now free.
Gamertag A remains linked to Microsoft account 3.
To complete the switch of gamertags between the two original Microsoft accounts, you must wait 30 days. After 30 days, switch Gamertag A from Microsoft account 3 to Microsoft account 2.
Example:
Gamertag B remains linked to Microsoft account 1.
Gamertag A is now linked to Microsoft account 2.
Microsoft account 3 is now free.
Cancel the Microsoft account that you created in step 2.
Example:
Gamertag B is now linked to Microsoft account 1.
Gamertag A remains linked to Microsoft account 3.
Microsoft account 3 is cancelled.
When you change your Microsoft account, your Microsoft Points are automatically transferred to the new Microsoft account.
You can move a gamertag to a different Microsoft account only once every 30 days.
This includes new gamertags downloaded from Xbox LIVE.
If you try to move a gamertag before 30 days have passed since the last time you moved it, youll get the following error message: