Ah right...
I actually cloned my site on the server, before even attempting the upgrade to 4.0 from 3.8.4. Placed the 'clone' in a new directory, and imported the database in to a new one. I only done it on the server because it is much quicker than downloading the whole lot, which would have taken hours!!!! I just used the SSH command line prompt, so it only took about 5 minutes.
I ran in to a few errors, but nothing that I could not easily fix.
Anyway, glad you got there in the end!