Follow these steps to change layer properties:
Use the example derived from the first example from Chapter 1, Getting Started with OpenLayers, also available at chapter04/2360_04_01_changing_layer_properties.html:
<!doctype html>
<html lang="en">
<head>
<title>Simple example</title>
<link rel="stylesheet" href="../assets/ol3/css/ol.css" type="text/css" />
<link rel="stylesheet" href="../assets/css/samples.css" type="text/css" />
</head>
<body>
<div id="map" class="map"></div>
<script src="../assets/ol3/ol.js" ></script>
<script>
var osmLayer = new ol.layer.Tile({
source: new ol.source.OSM(),
opacity: 0.6,
brightness: 0.2
});
var view = new ol.View({
center: ol.proj.transform([-1.8118500054456526, 52.4431409750608], 'EPSG:4326', 'EPSG:3857'),
zoom: 6
});...