Changing User Name

You don't own Minecraft on that account. If you need help with your account contact Mojang customer support: https://help.mojang.com

I don't understand. This is the email address I use to log into and play Minecraft. It shows all of my other info in the account page, but does not give me the button to change my username. My username is Rainbo6. It does not show up when I log in for whatever reason. But, when I play, my username is showing there. If I don't own it, how can I play it everyday by logging in with it? Please help. 

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From:"[Mojang] Kristoffer Jelbring (JIRA)" <[email protected]>
Date:Thu, Jul 30, 2015 at 3:47 AM
Subject:[JIRA] (WEB-50) Changing User Name

 [Mojang] Kristoffer Jelbring commented on an issue   Re: Changing User Name

You don't own Minecraft on that account. If you need help with your account contact Mojang customer support: https://help.mojang.com

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Mojang Web Services /  WEB-50 Changing User Name

I would like to change my user name, however the account page is not offering the option. Please see attached file.

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