Connect SQL Server Configuration Manager to set startup parameters to start SQL server in single user mode.
Click all programs and click on SQL Server, go to Configuration Tools folder and click on SQL Server Configuration manager.
Right click on SQL Server and click properties. Click on Startup Parameters tab. Type –m on Specify a startup parameter box and click add.
Click ok and you will see –m added. Click add and restart SQL services because this change won’t apply until you restart. That you will come to know by looking at the warning.
Restart SQL services.
Now connect SQL from SSMS as administrator. Right click on SQL Server Management Studio and select Run as Administrator option.
Connect SQL using windows authentication and navigate to sa login. You can reset the password on this account. Note it down once you reset it.
To test the new password, connect SQL server using sa account. It will prompt by saying the service is in single user mode. Go to configuration manager and remove the startup parameter we have added which is –m and restart services. Now test the connection with sa account with new password.