Delete character in file names

Hi,

I need a help to rename some of the files. i.e. delete some characters of a files.

eg. XX_5182179_ETERNITY_25TH_MB_AB_XYX_abc.ttjs

eg. XX_4182229_ETERNITY_21TH_MB_AB_XYX_abc.ttjs

like above eg. i have lot of files on a folder in desktop.

and I just want to retain only the blue highlighted text. and remove characters inbetween.  i.e. XX_51312179.ttjs.

I have this script.. but not doing nothing..

var myDoc = app.activeDocument;

var myPath = myDoc.filePath;

var myNEWName = (myDoc.name.replace(".indd",".ps"));

var myDc = new File(myPath+"/"+myNEWName); myDoc.save(myDc);

myDoc.saveACopy(myDc);

Please help me to achieve this..

Many thanks