Well, at the moment only administrators can delete user accounts:
(1) They visit user's profile
(2) Block the account by clicking on the button "Block User"
(3) Finally the button "Delete User" will show up and they click it to delete that account
That is, users have to ask website administrators to delete their account.
On the other hand, It's possible to let users delete their account; I mean, I've added that feature to a brand-new Q2A website, but it takes a whole bunch of customization either as a
plug-in or as core modifications.
The bottom line is each live Q2A website has somewhat diverged from what the Q2A platform currently offers and, in this case, this feature has to be implemented differently for each one of them.
Here's a discussion about letting users delete their accounts