Modifying the second level navigation arrow image

Open your master page.
Switch to Code View.

Search for "TopNavigationMenu". This should take you to the global navigation (top nav) instance of AspMenu.

Using Intellisense in the code view, or using the Properties pane, add the following property to the AspMenu tag:

DynamicPopOutImageUrl="insert image URL/path here"So your code should look like:

Runat="server"
DataSourceID="topSiteMap"
DynamicPopOutImageUrl="/images/myimage.gif" >