Navigate to ‘Administration’ on the left hand bar and then to 'User management'

Note you need to have Admin Rights to perform this step. 

Find the 'User' you wish to delete by either scrolling through the list or by using the search box. 

Click the ‘Delete’ icon on the right- hand side

Click ‘Yes, delete’ – Please note this cannot be reversed!

You can see who is the admin of your account under User Administration as well