This is an easy way to change the username of your wordpress admin account:

• login as your current admin user
• navigate to users > all users
• add a new user
• make sure the role is ‘administrator’
• give the user the desired username that you want

the next steps are:

• logout of your current admin account
• log back in as your new admin user
• navigate to users > all users
• delete your old admin user.