To change the layer settings in the Map Viewer, click on the Table of Contents (TOC) icon
Then select one of the layers, and click on the Settings icon
The Layer Settings panel looks like the one below.
The Layer Settings are divided in three groups:
In the General tab of the Settings Panel you can customize the layer Title, insert a Description and change/create the Layer Group.
Click on the Display tab to see what are the layer appearance properties you can configure.
The third tab is the Style tab. By clicking on it, an advanced Style Editor allows you to create new styles and to modify or delete an existing one. See the Layer Styling section to read more.