Taking Witto example a little further... Remove the semicolon on the move command when you are sure it will do what you want.

$strPath = "C:\Test\Test\"
$arrFiles = DirPlus($strPath,"/M _AC")
For Each $strFile in $arrFiles
    ? "Original File: " +  $strFile.Name " - "
    $renamed= "BG_STAT_" + $strFile.name
    ;move $strpath + $strFile.Name $strpath + $renamed  
    if exist($strPath + $renamed)
      "Renamed: " +$renamed 
    else
      "Error"
    endif
Next
_________________________
(... better days ahead)