First open your Microsoft SQL Server Management Studio.
Select ServerName and first select Authentication type is Window Authentication and Connect.

Now showing Object Explorer in left side.
In Security > Logins > Select your sql server authentication username.
And right click on username and select properties.

Now open login properties pop up and here you are set new password.

Enjoy..!

pertti jarvaPosted Jan 14, 2015, 3:22 PM
This only works in case your current windows account is also sa in the SQL Server which probably shouldn't be the case in normal installations. Of course if it's just your own setup on your own laptop that's a different thing.