Well, don't I feel like a doofus. Just after posting this I decided to change my password on the site to make it more user-friendly. After changing it, I decided to try the update again, I don't know why because I had just tried it three times in a row.
But there you go, it worked this time. Strange because I got past the password request every time I tried previously and it failed at the actual download/install section.
Fouth time is the charm I guess.
Cheers,
Graeme