May have found it on sourceforge

You should be able to upgrade from almost any version of concrete directly to 5.3.2

Make sure you take a backup of your site including database first.

But it said I needed to upgrade to 3.3.2 first as I'm running 5.3.1.1 at the moment on this site.

Yeah, you'll need to upgrade to 5.3.2
http://sourceforge.net/projects/concretecms/files/...

Then once that's all happy, dowload 5.3.3.1 and upgrade again.

sourceforge is less than easy to use..

here

http://www.concrete5.org/developers/all_downloads/...