Hello & Welcome to Just Answer,
Sorry to hear of any trouble with your device.
FIRST, let me recommend that you NOT be in any "hurry" to update the device, as these device usually come with relatively current maps and software. Plus, if you choose to update the maps, it can take a LONG time (an hour or more), even with a very fast internet connection.
Second, what I DO recommend is first CHARGING the device for a FULL TWO HOURS or more - using and AC adapter or the Vehicle power adapter. This is so that the device will have a GOOD level of charge - when it is time to update the software (or maps).
As for the "process" of updating, that is relatively simple. There is a program called Garmin Express that can be loaded on your computer and run, and once run, you will attach your device to the computer (via that USB cable you got) and the Garmin Express program will take care of any updates for you.
Let me give you a link to where you can get Garmin Express (below), And there is even a short video on that page that shows how to download, install, and run the program, and what to do and expect when you do that.
Click here --> http://www.garmin.com/express
Please let me know if all that makes sense, or if you have any other questions.
Thanks, ***** *****