Method 1:

Login into SQL Server using Windows Authentication.

In Object Explorer, open Security folder, open Logins folder. Right Click on SA account and go to Properties.

Change SA password, and confirm it. Click OK.

Make sure to restart the SQL Server and all its services and test new password by log into system using SA login and new password.

Method 2:

1.Open the SQL Server express management studio
2.Connect to SQL Server using windows authentication

3.Right click the server name and choose properties

4.Go to security tab. Change server authentication to “SQL Server and Windows Authentication mode”

5.Click OK and restart SQL Server
6.Go to SQL Server studio management express
7.Expand the server and choose security and expand logins

8.Right click on SA, from properties modify the password and confirm password

Method 3: (From Command prompt)

1. Start a command prompt by typing Start – Run – cmd

2. Enter the following commands, pressing Enter after each line

OSQL -S yourservername -E
1> EXEC sp_password NULL, ‘yourpassword’, ’sa’
2> GO

Where yourservername is the name of your server and yourpassword is the new sa account password.  Type exit twice to return to the server desktop.

Method 4: (Query) my personal favorite

Make a new query & write in it, then run.

Source code

USE [master]
 GO
 ALTER LOGIN [sa] WITH DEFAULT_DATABASE=[master],
 DEFAULT_LANGUAGE=[us_english], CHECK_EXPIRATION=ON, CHECK_POLICY=ON
 GO
 USE [master]
 GO
 ALTER LOGIN [sa] WITH PASSWORD=N’<insert_new_password_here>’ MUST_CHANGE
 GO