How to delete my domain account

Hi,

I am a global administrator for a domain account (XXXXX@XXX.onmicrosoft.com). This account is used for the Microsoft Windows Hardware Developer Program, where we have created some users. However, we have now applied for a new domain account (company domain), and we want to completely decommission the original domain account (XXXXX@XXX.onmicrosoft.com), including the users under it, because some of the content overlaps with the new domain account and we are unsure if there will be conflicts.

However, I cannot find this option in my interface. Could you please tell me how to proceed?

BRs,
Luke Chen