DECLARE @currUser varchar(100),
@SQL nvarchar(200)
DECLARE Users CURSOR
READ_ONLY
FOR select [NAME] from sys.database_principals
where 
[name] not in('dbo','guest','INFORMATION_SCHEMA','sys') AND
[type] in('S','U') AND
[name] = [default_schema_name]
OPEN Users
FETCH NEXT FROM Users INTO @currUser
WHILE (@@fetch_status <> -1)
BEGIN
SET @SQL = 'ALTER USER [' + @currUser + '] WITH DEFAULT_SCHEMA = dbo'
EXEC (@SQL)
FETCH NEXT FROM Users INTO @currUser
END
CLOSE Users
DEALLOCATE Users
GO
SELECT name as username, default_schema_name FROM sys.database_principals
 WHERE type in ('S','U') and name not in('dbo','guest','INFORMATION_SCHEMA','sys')