Admins with the necessary privileges can delete other people's accounts from their community website. In addition, members can delete their own account.
What gets deleted
Deleting an account deletes everything contained within the account, including:
All of its members
Because every member of the account is deleted as well, you may want to take a look at what happens when a member is deleted.
If you're an admin, you cannot delete your own account from the Admin Portal; rather, you'll need to delete your account via your account's settings (learn how).
Also, you cannot delete an account if one of its members is the only one with full administrative privileges.