After a login has been created, it may be necessary to change the password, default database, or default language. For example, a user may forget her password, want to change the password for security reasons, need to use a different database on a regular basis, or need to see messages in a different language.
Note If a user forgets a password, a member of the sysadmin or securityadmin fixed server role can change the password without knowing the original password. A user cannot change a password if he has forgotten it. Members of the securityadmin role cannot change the password of members of the sysadmin role.
To change the password of a SQL Server login