I wouldn't update your unit unless you have a Motorguide iPilot.
The update only addresses a few issues and most people aren't using those. Most of the time, people update and then realize it was a mistake and are begging to get back where they were. I've got 9Tg2 not the g3 model so I'm not sure of what version # your 9Tv3 is at, but IMO I would leave it alone until you've learned how to use it. No offense, but you having to ask how to change the downscan view tells me you need a lot of seat time to figure out how to navigate, set it up, save your favorites, etc.. There's some VERY good guys on Bassboatcentral.com under the LOWRANCE thread who can help you too. I would HIGHLY recommend that you get on YOUTUBE and watch as many "HOW TO" video's on Lowrance HDS Touch units. Most are good enough to help you learn the navigation menu's, the settings, etc.. to get you going. Once you're set up right, you'll leave it and just learn to find fish. When you get really good with it, fishing will become a "video game" and you'll be able to target fish and catch what you see on the HDS unit. it takes a lot of seat time to learn and understand what's there, but the HDS units make things alot easier than it was 5 years ago.
Let me know if you have more questions. And THANK YOU for your service!