Thanks, this worked for me to clear out both some A/P accounts and some A/R accounts. I named the account the same as the default A/P account (wasn't sure if capitalization and spacing mattered so I did the same captialization and spacing):

I then saw a message "Would you like to merge the two?":

In order for this to work I found that I had to uncheck the "Is sub-account" checkbox on the account I wanted to merge. I imagine you might also have to remove the account number from the account you want to merge; I did not test that hypothesis.