You can change the sa password by using einther Transact-SQL or To Management Studio
To change the sa password by using Transact-SQL
Execute the following statements to enable the sa password and assign a password.
osql -E -S yourSQLserverName
sp_password @old = 'oldpassword or null', @new = 'newpassword', @loginame ='sa'
go
To change the sa password by using Management Studio
In Object Explorer, expand Security, expand Logins, right-click sa, and then click Properties.
On the General page, you might have to create and confirm a password for the sa login.