How do I update this?You can't update it because Google Talk is discontinued and replaced with Hangouts. Visit the new product to find more information about it as well as downloads in order to start a video call.
Google Talk Video and Voice Plug-in supports most common browsers like Firefox, Chrome, Internet Explorer, etc. It is required so that you can make video calls to your contacts in Google Mail. It can also be used on Google Hangouts. You can make video conferences with up to 10 people, using this add-on.