A site I built years ago got hacked and I'm having to rebuild it from scratch - shouldn't be a huge issue as it only has 5 pages. I exported the ATO settings and on the new installation of WP, tried to import them into the latest version, but it wouldn;t work. Ended up having to install a really old version of Atahualpa - 3.5.0 - to be able to get the settings to import properly, and the site is kind of working now. Want to upgrade to a newer version though - I tried installing the latest one within WP but the settings didn't carry across. What's the best way to do this - presumably in stages?

you should be able to do that. attach a copy of the 3.5.0 settings