No, the player doesn't have a screen resolution settings panel. This means you can't change it directly, but there is a way to force it. Browse to the game or application that uses Unity, then save the whole page. You need to edit the HTML file that contains the Unity code and look for
width="---" height="---". Change both values in --- to the desired resolution (eg width="1024" height="768"). Save the changes and refresh the HTML file and it should be displayed using your values.