You cannot change the SA password in Microsoft SQL server like you do a users password.
To change the SA password you need to run the following command from a DOS prompt.
You will of course need to have some sort of SQL client installed.
C:> OSQL -E -S -dmaster -n -iC:\temp\sa.sql
where sa.sql contains
sp_password @new = 'will_never_forget_again', @loginame = 'sa'