Declare @UserName NVarChar(30)
Declare @Password NVarChar(30)
Declare @Application NVarChar(255)
Declare @PasswordSalt NVarChar(128)

set @UserName = 'AUSER'                 /* a user from aspnet_Users table*/
set @Password = 'AUSER_PASSWORD'        /* set a password */
set @Application = 'MyApplication'      /* from aspnet_Applications table, multiple apps can exist */
Set @PasswordSalt = (SELECT 1 PasswordSalt FROM aspnet_Membership WHERE UserID IN (SELECT UserID FROM aspnet_Users u, aspnet_Applications a WHERE u.UserName=@UserName and a.ApplicationName = @Application AND u.ApplicationId = a.ApplicationId))

Exec dbo.aspnet_Membership_ResetPassword @Application, @UserName, @Password, 10, 10, @PasswordSalt, -5