SniperWill863, you will need to update your Username and GamerTag on your profile. To do so, please do the following.
GamerTag: Click "About Me" on your profile (directly above), then click the yellow pencil next to "GamerTag", update it to your new GamerTag then "Save".
Username: Click "Help Desk" on the top right corner of the screen, then click "Request Login Name Change", type in your new GamerTag EXACTLY as it is spelled, then send/submit the request.
Thank you,
KoG FaceUp XS