Crude, but this will work, just loop through a directory (if you are able to execute xp_cmdshell, if not I'm sure there's a powershell script lingering around)DECLARE

@Filepath varchar(75),

@file varchar(25),

@Cmd varchar(150)

SET @file = 'test.csv'

SET @filepath = 'C:\'

SET @cmd = 'ren "' + @filepath + @file + '" "' + REPLACE(@file, 'csv', 'xls') + '"'

PRINT @cmd

EXEC xp_cmdshell @cmd, NO_OUTPUT

Why would you want to do this via TSQL?