Change layer names so lowercase

aaaa()
function aaaa()
    {   
    try {
        var i = get_layer_count();
        var end = 1;    
        var ret_ok = true;  
        while (i >= end && process_layer(i)) { --i; }
        return ret_ok;
        function get_layer_count()
            {
            try
                {
                var r = new ActionReference();
                r.putEnumerated( charIDToTypeID( "Lyr " ), charIDToTypeID( "Ordn" ), charIDToTypeID( "Trgt" ) );
        
                var ret, n; 
        
                try { ret = executeActionGet(r);                       } catch (e) { alert(e); ret_ok = false; return 0; }
                try { n   = ret.getInteger(stringIDToTypeID("count")); } catch (e) { alert(e); ret_ok = false; return 0; }
                r = null;
                ret = null;
                try { app.activeDocument.backgroundLayer; } catch(e) { return n; }
        
                return n-1;
                }
            catch (e) { alert(e); ret_ok = false; return 0; }
            }
        function process_layer(n)
            {   
            try {
                var r = new ActionReference();
                r.putIndex( charIDToTypeID( "Lyr " ), n);
        
                var ret, s;
                try { ret = executeActionGet(r); } catch(e)  { alert(e); ret_ok = false; return false; }
                var name = ret.getString(stringIDToTypeID("name"));
                switch (ret.getEnumerationValue(stringIDToTypeID("layerSection")))
                    {
                    case stringIDToTypeID("layerSectionEnd"):
                        break;
                    default:
                        var name = ret.getString(stringIDToTypeID("name"));
                        var name1 = name.toLowerCase();
                        if (name1 == name) break;
                        var d1 = new ActionDescriptor();
                        d1.putReference( charIDToTypeID( "null" ), r );
                        executeAction( charIDToTypeID( "slct" ), d1, DialogModes.NO ); // because of the bug at least in CS6 - CC2108 
                                                                                       // can't set layer name if layer is not active
                        ret = new ActionDescriptor();
                        ret.putString(stringIDToTypeID("name"), name1);    
                        d1.putObject( charIDToTypeID( "T   " ), charIDToTypeID( "Lyr " ), ret );
                        executeAction( charIDToTypeID( "setd" ), d1, DialogModes.NO ); 
                        break;  
                    }   
                ret = null;
                return true;
                }
            catch (e) { alert(e); ret_ok = false; return false; }
            }
        }
    catch (e) { alert(e); }
    }

see if this is right for you

// written by Lukasz Wieczorek at http://lukasz.io
// Please do not remove this and give credit if you repost. Thanks!
var layerLength = app.activeDocument.layers.length;
var docRef  = app.activeDocument;
for(i = 0; i < layerLength; i++){
   docRef.activeLayer = docRef.layers
   var myName = app.activeDocument.activeLayer.name;
    var newName = myName.toLowerCase();
    docRef.activeLayer.name = newName;
 }