RESET "SA" PASSWORD (SQL SERVER)

USE MASTER

comando :

sp_password @ old = null, @ new = 'complexpwd', @ loginame = 'sa'
go 

Altro modo:
http://deepakrangarajan.blogspot.com/2008/01/forgot-sa-password-in-sql-server-2005.html

How to resetting the sa password on SQL Server

Yousef_Alahmad (IT Manager) posted 2/24/2010 | Comments (0)
When creating a new SQL user or changing an existing user with the SQL Server Management Studio, you'll need do run a few queries to get around the default expiration policies:

ALTER LOGIN [user] WITH PASSWORD='pa$$w0rd' UNLOCK
ALTER LOGIN [user] WITH CHECK_EXPIRATION=OFF
ALTER LOGIN [user] WITH CHECK_POLICY=OFF