The tax wizard defaults my filing status to head of household. I need to change this to single. I know I did this last year, but can't remember how to access it.

Why don’t you want to file Head of Household if you qualify?  Head of Household is better than Single.   Turbo Tax automatically gives you Head of Household when you enter a qualifying dependent.   Go back through My Info or Personal Info and check the answers to your dependents.