Deleting 2nd admin user account

My husband and I used to share a computer. I was the admin. Then I got my own macbook and changed him to the admin but stayed on as another user. BUT.....when I go to user groups in preferences we both have admin by our user account names although mine is grayed out. I want to delete my user account completely trying to free up more room on the computer for his use. User Group will not let me highlight my name (with admin next to it) in order to try to delete it. What should I do to get rid of my old account? Thanks....