Discourse.net

I think you need to get to a 3.x version first, and from there you can leap to 4.x.

I found the change from 2.x to 3.x the most traumatic because the underlying architecture changed the most, necessitating changes to public templates and stylesheets and also changes to my basic underlying installation/setup (although YMMV depending on how you have your blog installed), but once I got that all squared away I was pretty happy with the upgrade. The jump from 3.x to 4.x was much easier to do and hardly affected the public face to my blog, but it drastically changed the blog administration screens and in a way that still annoys me...