BigJig,
Welcome to the forum. You only need to download the latest or "highest numbered update". The others are there for people who may need reinstall a past update. You can of course register your unit with humminbird and download the latest update from there also.
We only keep the SideImaging Unit updates here on the forum, so if you have other HB units you would have to go there to get the updates.
Good Luck, and again, welcome to the forum!
Robert Gecy
Forum Administrator