How do I use Microsoft points to change my Xbox gamertag

Depends on what you mean by Microsoft points. Microsoft points were discontinued in 2013 and they started to use a currency system.

If you mean Reward points, you would need to redeem Xbox gift cards and redeem enough to cover the amount of the change.

If you mean gamerscore, that has no monetary value and can't be used for purchases.

[quote user="PizzaSamurai"]How do i change gamertag ? Do i have to log on from the xbox, or can i do it online? Im afraid to do it on the xbox out of fear of deleteing the achievements on there from the new account.[/quote]You
can only change it on the Xbox console

1. Sign into the Xbox using the gamertag you want to get the name from.
   
2. Click on your gamertag on the 'Dashboard'
3. Select "Change Gamertag".
4. Chose a different name
5. Pay 800 Microsoft Points to change it.

That has freed the name you want to use.

1. Now sign in with the gamertag you want to put the name on.
   
2. Repeat steps 2 and 3 from above
3. Choose the name you want to put on your gamertag
   
4. Pay another 800 Microsoft Points to change it.
   

• 
  

Note: You will need 800MS Points on both accounts (1,600 MS Points total) in order to change the name into one you are already using. You will NOT have to pay the 800 MS Points if you are changing the name from a name you were
automatically given.

Hello,

You'll need 800 Microsoft points in order to change your gamertag. Please follow this page on how to change your gamertag.

support.xbox.com/.../change-xbox-live-gamertag

I’m not sure if you can use points to change a Gamertag. First time is free, second time is $10.

Here is how you do so depending on device.

https://support.xbox.com/en-US/my-account/manage-gamertag-and-profile/change-xbox-live-gamertag

The txt quoted is in the section which yes has the Windows LIVE section below, but at the top clearly states Xbox 360 Console:

"How to change your Xbox LIVE gamertag

Change your gamertag on your Xbox 360 console

You can easily change your Xbox LIVE gamertag. If your gamertag was created for you during Xbox LIVE sign-up, you can change the gamertag once for free. Additional Xbox LIVE gamertag changes cost 800 Microsoft Points.

To change your Xbox LIVE gamertag

On your Xbox console, sign in using the Xbox LIVE gamertag that you want to change.

Go to Social, and then select your gamertag.

Select Change Gamertag.

Note the Price of the change, and do one of the following:

Select Enter New Gamertag. If the gamertag you enter is already taken, you will be prompted to try another gamertag.

Select Get Suggestions to view possible gamertags.

Once you enter or select a new gamertag, select Yes, use this gamertag.

Note Click Add Microsoft Points if you don’t have enough points to complete the purchase.

Once you confirm your new gamertag, the change is reflected across Xbox LIVE. You don’t need to tell your friends that you changed your gamertag — their friends lists will be updated automatically."

Again a clear statement from Microsoft, it should be honoured not dismissed.