Firstly, you cannot change the username on Reddit using the same account. So read the steps below to understand if that is something you would like to achieve and then do it. Make sure you are on the account tab and then click on the change button next to your email address. By doing this, you are not deleting your account but instead changing the email address. This way you can create a new account with your old email address. The next step is to confirm your new email address.