MS SQL Server: assuming the instance and user name to be NETX_SERVER_SQL and sa, respectively, do:
Open a command window, cmd.exe, and enter following command
osql -S .\NETX_SERVER_SQL -E
On the osql prompt enter
1>sp_password NULL, 'new password', 'sa'
2>go
1>exitMake sure you also change the password in your BMS workspace (BMS Studio / Server / System Configuration / XDB Parameters / Database password).