Post categories

The database table wp_term_relationships relates the object_id (post or link) to a category or a tag in wp_term_taxonomy which in turn relates to the actual description and slug in wp_terms.

So how do I EASILY change it.

Change what?

I have a database backup from wordpress v2 and want to easily import it into wordpress 2.3.2

It doesn’t work like that.
You export/import between the same versions. After the successful import you do the upgrade.