I’ve just upgraded a forum for a client to the latest release candidate for phpBB3, and was pleasantly surprised by how easy it was to do, even with a few modifications to the phpBB2 powered forums.

The process is well documented on the phpBB website - but I’ll give a quick run down here.

1. Install a clean copy of the latest version of phpBB3 (RC3 at the time of writing) to a new directory on the server - I used /phpbb3/ for this, as I planned to rename it back to /forums/ after the upgrade was complete.
2. Verify everything is working with the new installation.
3. Use the convert script to import all posts and settings from your existing phpBB2 installation (this does not make any changes to the phpBB2 installation or database, so if things go pear shaped, you can try again). The convert script is accessed via the new ACP (Administration Control Panel) in phpBB3.
4. Check that everything is working, and remove the phpBB2 installation.

The most impressive part of the process is that all attachments which were added to the phpBB2 powered forums via attach mod were migrated to the new built in attachments system in phpBB3!