Look for code changes to upgrade style

Hello,

I created some WP themes but they are mostly 2.9.1 compatibile (or 2.9 and 2.8.6). I am looking for some code changes which help me to update my themes, or whatever what could help me.

I am creating also phpbb3 templates and modifications and there are code changes for each version of phpbb (for php files, languages and styles), so I hope there are some also for WP.

Thanks a lot,
Kamahl