Thanks for all the responses, I know what to do next time I play.

I've only played about 5 hours so far, and am enjoying it. So looking forward to trying out the new version.

I just bought the game a few days ago, but I just wanted to explain what I've spent the last 1.5 hours doing, and how frustrating it's been. So I go to play Factorio (via Steam) and it tells me I need to update. That's fine, my wifi is a bit dodgey, so I go and plug into the router, and it downloads...