The easiest way to update the player is by downloading the latest version from its official website.
Access the page, download the package, close all your browsers and launch it. This is the safest and easiest way to update he plug-in when you encounter errors. However, if it gives you errors, go to Start > Control Panel > Programs > Uninstall a Program and uninstall the player completely, then install it.
Download page: https://unity3d.com/webplayer