Help editing a script

Hi,

Very nearly found a solution to this old problem I have. I've found a script that saves groups as PNGs and it's great but I need it to save to JPEGs instead. I also need to have an option to change the name. In the script is fine although I did like the 'export layers to files' pop up box. They are currently named after the group name which I want to keep, just add to. I'm really sorry for my lack of experience when it comes to stuff like this, I know people have suggested ways to do it but I can't understand how to edit the script itself and get it to work.

Many many thanks in advance!!

#target photoshop

function main(){

if(!documents.length) return;

var doc = activeDocument;

var oldPath = activeDocument.path;

for(var a=0;a<doc .layerSets.length;a++){

activeDocument.activeLayer = activeDocument.layers.getByName(doc.layerSets[a].name);

dupLayers();

activeDocument.mergeVisibleLayers();

activeDocument.trim(TrimType.TRANSPARENT,true,true,true,true);

var saveFile= File(oldPath +"/"+doc.layerSets[a].name +".png");

SavePNG(saveFile);

app.activeDocument.close(SaveOptions.DONOTSAVECHANGES);

    }

}

main();

function dupLayers() {

    var desc143 = new ActionDescriptor();

        var ref73 = new ActionReference();

        ref73.putClass( charIDToTypeID('Dcmn') );

    desc143.putReference( charIDToTypeID('null'), ref73 );

    desc143.putString( charIDToTypeID('Nm  '), activeDocument.activeLayer.name );

        var ref74 = new ActionReference();

        ref74.putEnumerated( charIDToTypeID('Lyr '), charIDToTypeID('Ordn'), charIDToTypeID('Trgt') );

    desc143.putReference( charIDToTypeID('Usng'), ref74 );

    executeAction( charIDToTypeID('Mk  '), desc143, DialogModes.NO );

};

function SavePNG(saveFile){

var pngOpts = new ExportOptionsSaveForWeb;

pngOpts.format = SaveDocumentType.PNG

pngOpts.PNG8 = false;

pngOpts.transparency = true;

pngOpts.interlaced = false;

pngOpts.quality = 100;

activeDocument.exportDocument(new File(saveFile),ExportType.SAVEFORWEB,pngOpts);

}