It’s not complicated at all. Just go to https://www.tomtom.com/ and sign up for your account using a valid email address. Then go here: https://www.tomtom.com/en_gb/mydrive/ and download the MyDrive Connect application and install it. After installation, log in to your app using your account and connect your GPS to your computer through its data cable. Now the update should start automatically, if not, you have a manual button to update it by selecting what you want to update in a list.
I warn you that you need a lot of patience. Updating is a process that could take a lot of time depending on your Internet connection. So do not be impatient if you see it’s moving too slowly. Good luck!