I have installed MSSQL 2012 on Windows 2012 Server using the following settings:


But when I try to login (The username is my local user that I log-on to windows 2012 server with) I get (default instance name = MSSQLSERVER):


I have looked at:
How can I change from SQL Server Windows mode to mixed mode (SQL Server 2008)?
http://vsstack.blogspot.in/2013/11/microsoft-sql-server-error-18456-login.html
but that guide assumes there is already a DB available that I can enable authentication for. This is not the case. What am I missing? Do I need to re-install MSSQL to select Mixed Mode?
EDIT: In this case it seems its only possible to change to Mixed Mode by messing around in the Registry, bummer: http://www.top-password.com/knowledge/sql-server-authentication-mode.html
AND BUYING this http://www.top-password.com/purchase.html
to update the sa password afterwards. Maybe they should consider writing that as a warning in the installation wizard!
It will take a couple of days to uninstall MSSQL 2012: https://www.youtube.com/watch?v=FvjjU8nPrRc
So maybe the best solution is to re-install windows?