ATT.com/myprepaid

I am trying to access the online access to our account.  They keep sending temporary  digit pin codes to the account.  I would like to get away from temporary to permanent pin codes.  How can we make a permanent change?  They are sending emails with no relevant information in them such as actual passwords or pass pin code.  I understand the new security measures being necessary.  I am just looking for common sense answer to my request.  Thanks.