how do you delete gamertags on xbox?

Major Gamertag Changes Coming to Xbox Live – New Features and System Explained

Here’s how:
Go to Settings, and then select System.
Select Storage.
Select All Devices.
Select Gamer Profiles.
Select the gamertag that you want to delete.
Select Delete.
Select one of the following:

How To Delete A Gamertag On Xbox One Without Access to the Console (Remotely)