To delete the "Sheet1" through "Sheet2" of all the workbooks within "D:\XLSFiles\" the following syntax would be used:
ConvertXLS.EXE /S"D:\XLSFiles\*.XLS" /T"D:\XLSFiles\*.XLS" /P103 /1"Sheet1" /2"Sheet2"
Note: You don't have to specify Boolean (TRUE/FALSE) parameters that are FALSE. Nor do you have to specify parameters that are empty.
The /S and /T switches specify input and output workbook respectively, which in this case is the same workbook. You can also specify subfolders with the /R switch.