Need to Delete an Xbox account

1. Press the Xbox button to open the guide.
2. Select System, then Settings.
3. Select Account, then Remove accounts.
4. Select the account that you want to remove, then select Remove to confirm.
5. When you're finished, select Close.

activision only allow you to change linked accounts every so often, i would contact the support for them to sort this, if you disconnect your account you may not be able to play, or you could just create a new cod account and link your account to that
instead, this will obviously destroy any saved progress and ranks though.

and another one that does not actually read the post and actually understand it.

Hey there, it's actually not possible to delete an account from Xbox Live's servers by request. What I suggest you do though is switch this gamertag's (which you're posting on) Microsoft Account to a new one, then change your primary gamertag's Microsoft
Account to the one you're now posting on.

Instructions to do so can be found
here.

If you want to outright delete the account contact support using this link:
support.xbox.com/contactus

However, if you wish to keep this account as a secondary account, you can switch the e-mails / Microsoft Accounts associated with each by following the diections found here:

support.xbox.com/.../switch-gamertag-to-different-microsoft-account

EDIT: Ninjad by Mad Cow